Metric vs. US model of HP 50g



#79

From the HP 50g Data Sheet (HP #4AA1-0865ENUC, June 2007), I see that those of you in the rest of the world get a much smaller model of the HP 50g than the one here in the US:

Size (L x W x D) 7.24 x 3.47 x 0.98 cm (18.4 x 8.8 x 2.5 in)

It is surprising that there isn't more difference in mass: 196g for the metric model vs. about 250g for the US model, assuming that the specified weight of 8.8 oz was measured in a 1G field.

Since the metric model is too small, and the US model is absolutely huge, I think I'll stick with my HP-48GX. :-)

Edited: 28 Jan 2010, 1:04 a.m.


#80

d:-D

Wasn't there a Mars probe crashed for similar reasons once upon a time? Leave Myanmar alone, go metric.


#81

Does Liberia also use these outdated units? :-)

- Pauli


#82

Thanks Pauli, I felt there was another high tech country missing. But now we´ve got all of them d;-)


#83

Yes, and the US Stock Market switched from fractions to decimals and it crashed shortly thereafter. ;-)


Regards,


John


#84

Ahhh, that was the reason ... so far I thought it was caused by some (many, most?) bankers going crazy. Thanks, John, for pointing us to the true cause. Where else could we expect such an enlightenment?


#85

There is one solution to the stock market, financial bubbles, excessively large numbers, computer viruses, communism and famine: Base 60 is all we need to fix all the problems of the world.


#86

Quote:
Base 60 is all we need to fix all the problems of the world.

Some of my middle school students have trouble adding 3194 and 4287. Please don't make them add Cr2Mg1A and 5JetMM0.


#87

Actually, I misspoke.

It should be base 43:

http://www.newband.org/instruments.htm#partch%20instruments

#88

The fact that the US has not converted is frustrating to me. In all of my science classes in school in the 1970's we used the metric system exclusively. However in university engineering classes the professors used our US / British based units. 30 years later we are still in limbo using a mix of both systems. What will it take to finish the conversion? Maybe we are waiting for the US to win a football World Cup. ;-)

Regards,

John


#89

>What will it take to finish the conversion?

The sad reality is that it will probably take the US losing a war and having our factories bombed to a point of destruction equivalent to what happened in Europe in the World Wars.

Doing a real change to the metric system takes real money. Imagine all the lumber mills changing all of their hard tooling to make plywood in 5mm, 10mm etc. sizes. Also the steel mills will have untold amounts of tooling to change. Every paper maker will have to change all it's dies to make A4 paper vs. 8.5x11" and then all the envelope manufacturers have to change their tooling to accept the A4 paper in different folded configurations. Every machine that processes paper will have to be changed.

How about changing every road sign in the US AND where it is placed so we don't have stupid signs that say "1.61 km to Exit"

The auto industry does most thing in metric because they change their tooling every few years and they would pay that cost regardless of the dimensions of the parts. They convert to US units for their advertising and marketing specs printed here but they design and build in metric.

The bottled beverage industry is more and more a metric dominated field. For a long time it was the lonely 2 liter pop bottle that was the only purely metric consumer product here in the states. Now most plastic water bottles and many wine bottles are in true ml designations. But guess what, the hard tooling for plastic blow molding wears out from constant temperature cycling of hot plastic and cold air. Since they are changing it on a regular basis anyway it can be made metric easily.

I'm not sure but I'd venture to say that most of our toys here that come from China are made to standard metric dimensions.

We can talk about history, or tradition of bullheadedness but, just like the calculator market, it comes down to cold hard cash.


#90

Quote:
We can talk about history, or tradition of bullheadedness but, just like the calculator market, it comes down to cold hard cash.

While both may be true, OTOH there may be a lot of cash saved. Thinking of global players producing material for more than only the US of A: they may discard their Imperial tools after next maintenance interval. And there are further advantages: e.g. paper may be cut in A0, where from A1, A2, etc. are easily made by cutting in halves repeatedly. No heaps of waste paper anymore. - No need to memorize strange conversion constants, in particular in geometry. Etc. as discussed here ad nauseam.

For the traffic signs, let the miles die last - nobody will care.

#91

John, I wouldn't hold my breath waiting for the US to convert to metric. Just ain't gonna happen. We know our inches and feet and pounds and we like them. We teach our kids about the metric system in school, but it is soon forgotton because it is rarely used here. We put up with liters sometimes, but we don't like them.


#92

Quote:
We know our inches and feet and pounds and we like them. We teach our kids about the metric system in school, but it is soon forgotton because it is rarely used here. We put up with liters sometimes, but we don't like them.

I live In Iowa, USA and would much prefer if all measurements were metric. I like liters, not quarts.


#93

Any engineer in the US, especially if younger than what--50 or so?--is perfectly happy in either system. It's what we do. The measurement system is trivial and arbitrary compared to the real problems.

Liters are no "better" than quarts, and in fact they are so similar in absolute size that, like the meter and the yard, you can be roughly familiar with either from the other.

What I like most about or customary units is that they are almost all one syllable words.

quart
pound
inch
foot
yard
slug
ounce
peck
pint
rod
chain
league
furlong (oops, 2 syls)
bushel (oops, 2 syls)
gallon (oops)

compare to
litre
kilogram
newton
centimetre
meter
millimeter
gram (finally!)
pascal (ok I guess that is shorter than PSI but it doesn't mean
anything unless you say newtons per square meter...)

#94

First down and nine meters to go?

#95

How about the so-called "Gimli glider," an Air Canada jet that ran
out of fuel and nearly crash-landed but for the skill of the pilots, due (in part) to confusion between US and Imperial gallons.
It's a great story about compounding of errors. Makes one wonder why the 50g has both "mi" and "miUS" where 1_mi = .999998_miUS .
Love that old engineering joke about "furlongs per fortnight" !
cheers, Glenn


#96

Why two miles? Those pesky surveyors! :-D

TW


#97

I corresponded with a British lady when they made their conversion to metric, She called her new decimal system of currency metric. I remember changing a pound note to coins, I got 9 coins and looked stunned, so the lady said I have given you 5 shillings and 4 half crown. live nd learn. Then there was the octagonal thruppence for telephones. They got over it, why can't we? Sam Levy in San Diego


#98

But the old currency was actually easier to divide and handle in your head. 10 divides evenly only one way. 12 divides into thirds, 4ths, halfs, 6ths. The 20/12 system made possible all sorts of equal divisions.

In decimal, it is "easier" except that it isn't.

As physicists would say, choice of base system is "trivial."

So then why is base 10 so good? Only because you are used to it!

Edited: 28 Jan 2010, 12:32 p.m.


#99

Quote:

So then why is base 10 so good? Only because you are used to it!


http://www.youtube.com/watch?v=BblsNzx6yEk


Oh my god, I remember that! I haven't seen that since the days of the HP 35!

How many fingers do you have?

And toes??


Hi Ángel!

I know two people with 11 toes...

And I have 8 fingers....

~~~:)


aha! that explains a few things... :)

I actually flew the "Gimli Glider" before it was retired from service last year.

Fuelling in an imperial measure with metric units in an aircraft
with correct sensing fuel gauges as well as fuel flow guages.

1. First, while sitting in the cockpit, the fuel guy hands you a
receipt in gallons or litres of Jet A fuel loaded.

2. This gets converted by multiplying with a specific gravity (
S.G.)to kilograms of fuel. The guages are in kilograms in
Canadian Aircraft. The S.G. is temperature specific and varies
each day. The fuel remaining in a tank is usually cold from
altitude to landing and the S.G. will not be the same as the
loaded fuel. Fortunately the fuel remaining in tank after landing
is usually a percentage of the fuel loaded for the next flight and
therefore has a small error to the total calculations.

3. Add the fuel on board (FOB) at landing to the converted to
kilograms fuel boarded (TENDERED FUEL) and you have the total fuel.

4. Ways to check fuel consumption in the air. Five hour (Toronto
to Vancouver B767) flight times on average 5000 kg/hour and you
will burn 35,000kgs. The average varies due to weight of
aircraft, winds and etc. This plus operational taxi fuel, holding
fuel, alternate fuel, approach fuel, 5% slop fuel and you may have
45000 kgs on board. So if all goes correctly and you arrive on
sched as planned then you should have approximately 10000 kgs
remaining. The guages will do an analog or digital calculation
based on sensors in the tank, temperature and display kilograms
remaining (Fuel in tank). The computers using fuel flow will
calculate the fuel in tank by taking the original FOB and
subtracting the fuel flow versus time (calculated fuel in tank).
This is all displayed info in the aircraft.

NOW for the Gimli glider:

1. New aircraft to the fleet and relatively new to Canada
operations and the MOT (our FAA). Also the first Aircraft in
Canada at AC with metric guages.

2. Fuel guages inoperative at the gate so no display of fuel.
Fuel guages at the wing fuelling points also unservicable. Fuel
flow system inoperative so no calculated remaining fuel
indication. Not a problem usually, as one has drip sticks that
will measure the depth of the fuel in the three tanks and can be
accessed after fueling. The sticks WERE in inches at the time of
purchase. The Air Canada charts had been converted to metric so
the inches on the sticks had to be converted to cm on the chart by
maintenance in conjunction with the fueller who was delivering
fuel by the litre which had to be converted to kilograms with an
S.G. The mistake was made at the conversion of depth of fuel in
inches to cms by maintenance.

3. No indications in the air as to actual fuel via guages on
tanks or fuel flow on board and since the error was made at the
drip stick measurement, the incorrect total fuel on board was
delivered to the pilots. They followed the book by using the
maintenance procedure to measure fuel in tanks with the drip
sticks. As a result, they did their rough math of X amount of
fuel divided by the average for the flight and came up with
sufficient. This would normally be compared to the onboard system
which will display insufficient fuel but did not due to a KNOWN
technical problem which pecipitated the drip stick measurment by
maintenance.

4. Rectification. Well every where we go we get fuel loaded in
litres except for the US. All guages on the aircraft are metric.
Conversion is done from gallons to kilograms based on the S.G.
No aircraft can be dispatched with a multiple fuel indication
failure now. At least one of the systems must be in place as a
check against the fueler, aircraft, pilots and maintenance.

The aircraft should be controllable in any loss of all engine circumstance, the skill entered when the F/O new of a decomissioned airforce runway which was obtainable in the glide, otherwise this aircraft would have landed in a field. Instead it was repaired and flew until 2008. By the way, an B767 should glide about 90 miles if at 30,000 feet.

Kind of an extremely reduced synopsis of the situation. But it sure does indicate how complicated a simple system can become:

Inches to cms, cms via a chart to kilograms, fuel boarded in gallons converted via SG to kilograms. Broken fuel guages system including the fuel flow system and both sets of guages; cockpit and wing fuel point.....

Cheers, Geoff

p.s. I am doing this from memory as I was at Canadian Airlines at the time of the incident. The problem is the fuel was boarded ultimately in pounds and labeled kilograms. So 27000 pounds incorrectly labeled 27000 kilograms would equate 12,244 kilograms. Well short of the required fuel!

Edited: 30 Jan 2010, 3:58 p.m.


Geoff,

Could they have been warned, or at least curious, at how long (or how far down the field they went) until Vrot? Do you calculate that for every take off? Must depend to some extent on mass of the plane. Would the missing ~13000 kg have made a noticeable difference (depends on the mass of a 767, I guess)?

I time every takeoff when I'm riding commercial. If we ever get to 40 seconds before the plane actually lifts off, I'm getting ready to run for the exits! Does that sound about right?

All my own take offs & landings are in C150/172/177 - where a few hundred pounds DOES make a difference.


Hi Dave.

40 seconds sounds about right for a heavy weight takeoff for any airliner. It depends on thrust to weight to lift ratios.

For example 777 engines on a 737 then 40 seconds would be to long ;-)

Vr (or V rotate) can take a while at a max takeoff weight.

Getting back to the 767 the entire feel of the aircraft is artificially induced via feedback to the control column by what is known as the Q-feel. In the C150/172/... this feedback is due to the direct input of the airflow on the control surface through cables to the control wheel. In small, medium and heavy airliners the feel is artificial.

So having less weight in the aircraft would have made it marginally more nimble but not noticeable through the controls. Also Vrot should have been reduced due to the lighter actual weight. Vr would have been calculated based on:

1  weight
2 temperature
3 air pressure
4 runway surface condition
5 wind
6 climb gradient
7 V2 calculated speed

As such and combined with whether the crew elected to takeoff off with a calculated 'reduced thrust'(see below) then the difference in weight would have been masked by the other conditions. Suffice to say, every takeoff off at the same takeoff weight, based on the above list would result in a different feel.

reduced takeoff is the thrust calculated to safely get the aircraft airborne while considering runway length, stoppability on the runway prior to V1 and numerous other factors including runway contamination. In effect if all parameters allow it, it results in a thrust setting set lower then max power to save on engine wear. Again a short description!

Cheers, Geoff

p.s. the 777-300 that I fly weighs approximately 725000 pounds at max takeoff (Vancouver - Sydney non stop) and a shortage of 17000 lbs would not make any difference in the feel of the aircraft at takeoff thrust!


Edited: 30 Jan 2010, 8:04 p.m.

Geoff,

Do you know if the maintenance crew was aware that the fuel gauges and flow sensors were broken, and thus how critical their measurements and conversions were? I wonder if they were being sloppy because they thought that all the other systems would catch any error.


Without casting dispersions, not the intent here as the entire procedure was new.

The reason one 'drips' the tanks is because any single element in the fueling system is suspect. New aircraft, new systems, new requirements for trouble shooting.

To put it in perspective a few definitions are required.

1 MEL or the minimum equipment list. This is a list of items which are required for the dispatch of an aircraft. For example on a two engined aircraft there are 4 generators. One in each engine, one in the Auxilary Power unit (a small get engine used for ground or air power and adjunct to pressurization if required do to abnormal operations) and a RAT (ram air turbine) which deploys automatically or manually in flight to supply both hydraulic back up and electrical power in the event of a loss of both engine generators and APU. The question arises, one generator is not working due to a known fault. Do you ground the aircraft. Well, here there is no need as you can run the APU in the air and on the ground to cover for the failed generator. Flights will be restricted to over land only and subject to other rules, to much to cover here. Also one generator through switching is sufficient to run the entire aircraft if required. So the MEL may say "fix at main base within x days and run the APU to cover the failed engine systems.

2 the Fuel system (767): composed of six pumps, three tanks, Fuel gauges for 'total in tank', 'fuel flow', 'fuel used', system for inflight and onground determination of amount, calculating system for total fuel minus fuel used, on board display, fuel wing area display for ground personel and more.

3 The MEL by Boeing and AC state that a drip is required if any single system has failed. This will cover the aircraft to the next maintenance cycle as dictated in the MEL. The crew would have determined that a drip was required and directed maintenance to proceed with the external drip.


The point is that the drip was done as per the MEL to cover what in affect was a total system indication failure. It would not have been done on a functional system. Aircraft today do not dispatch on total system failures regardless of the drip test availability thanks to this incident. In fact, if any single gauge is U/S (unservicable) a drip is required.

So my assumption is that due diligence was exercised by maintenance as per the MEL and that the conversion error was due to other failures; metric ignorance, misplaced decimal position (calculator or hand done conversion?) or something else....

Cheers, Geoff

Edited: 30 Jan 2010, 10:22 p.m.

Quote:
How about the so-called "Gimli glider," an Air Canada jet that ran out of fuel and nearly crash-landed but for the skill of the pilots, due (in part) to confusion between US and Imperial gallons.

I think that was more pilot error anyways. Yes there are some that refer to the old Imp. Gal but 99% of the people I met always use the American Gallon here in Canada.

I learned the metric system first due to the governments regulations that prohibited teachers from teaching the SAE/Imp system (thankfully reversed in the last year or so). Then I learned the Imperial system in high school. I now don't understand what makes the SI system so much "better". Its a measurement system be it meters, inches or corn cobs if its got a base measurement and a standard increment rate, does one become better then the other?

Dimitri


Quote:
I now don't understand what makes the SI system so much "better". Its a measurement system be it meters, inches or corn cobs if its got a base measurement and a standard increment rate, does one become better then the other?

Exactly that's the point: SI is a measurement SYSTEM - the Imperial collection is a heap of mostly unconnected measures. As I said in another post in this thread, this was discussed in this very forum several times ad nauseam already.

HTH

Walter


The imperial measures are connected:

1 mile = 1760 yards

1 acre = 43 560 square feet

1 US gallon = 128 US fluid ounces

Easy, isn't it? ;)

Edited: 4 Feb 2010, 6:51 a.m.

Quote:
the Imperial collection is a heap of mostly unconnected measures.

3 teaspoons to a tablespoon.
2 tablespoons to a ounce.
8 ounces to a cup.
2 cups to a pint
2 pints to a quart.
4 quarts to a gallon.

3 grains to a inch.
36 grains or 12 inches to a foot.
36 inches or 3 feet to a yard.
5,280 feet or 1760 yards to a mile. (which is a 15 minute walk)

7000 grains or 16 ounces to a pound.

It all interrelates, and the above is simply from memory. Its just another system. Based on the grain (weight, distance and fluid volumes) but still a system non-the-less.

Dimitri


Well:

Distance: 1km = 1000m, 1m = 1000mm, 1mm = 1000µm, 1µm = 1000nm, ...

Area: 1km^2 = 100ha, 1ha = 100a, 1a = 100m^2, 1m^2 = 100dm^2, 1dm^2 = 100cm^2, 1cm^2 = 100mm^2, ...

Volume: 1m^3 = 1000dm^3, 1dm^3 = 1liter = 1000cm^3, 1cm^3 = 1000mm^3, ...

Mass: 1Mt = 1000kt, 1kt = 1000t, 1t = 1000kg, 1kg = 1000g, 1g = 1000mg, 1mg = 1000µg, ...

Force: 1N = 1 kg*m/s^2

Pressure: 1Pa = 1 N/m^2

Energy, work: 1J = 1 N*m = 1 V*A*s

Power: 1W = 1 N*m/s = 1 V*A

I could go on ... but it's sufficient to see the *slight* difference between a system and a so called "system", isn't it?

Edit: For everyday "household" use 1m = 1 big step, 1km = 15 minutes comfortable walk, 0,3l = a big cup or a good glass of juice, 0,5l = a good jar of beer, 1l = the same in Bavaria :-) , 1kg = the "weight" of 1l Bavarian beer, 10N = the weight of the same ;-) , 2kJ = the energy contained in 100g of Swiss chocolate = 1 bar of chocolate, etc.

Off household approximation: Speed of light = 3e8 km/s = 30 cm/ns d:-)

HTH

Walter


Edited: 6 Feb 2010, 12:25 p.m. after one or more responses were posted


Quote:
I could go on ... but it's sufficient to see the *slight* difference between a system and a so called "system", isn't it?

I get what you are saying however once you learn a system it makes no difference. At least for me in using both, going from one to the other or at the same time if I need to. Numbers are numbers if they are defined you can work with them even if its not terribly efficient adding .654" to 142.56mm if both are given.

Dimitri


Quote:
once you learn a system it makes no difference. At least for me in using both, going from one to the other or at the same time if I need to. Numbers are numbers if they are defined you can work with them even if its not terribly efficient adding .654" to 142.56mm if both are given.

Every grown up person on this very planet has the right to make his/her life as complicated as (s)he likes. Maybe, however, (s)he will learn about other people working more efficiently and the tools they use. Then, (s)he is free to return to sentence 1 d;-). Maybe that helps.

Walter

P.S.: Most administrations support their citizens in that quest. 3 of 200 do not d:-/.

Edited: 6 Feb 2010, 11:41 p.m.

A global view...

Greetings,
Massimo


Although a nice map of countries that adopted the metric system, Canada should be neither color. About the only thing that is not dual system is our traffic signs. From filling government forms, going to the doctors or buying food everything here is dual system. Which my be why I got this view on the matter.

Dimitri

Just 'cause everybody's doin' it don't make it right.

We get along just fine. And we actually are (along with Canadians bet even moreso than them) the only engineers on the planet who 1. can work in multiple units and 2. Are able to directly utilize a vast body of previous work without having to convert everything.

Seriously, when we trade internationally, we use metric. We make a lot of metric stuff in the U.S. and always have. Note that it is in "customary" measure that you find all the odd stuff. In engineering we are heavily metric in the U.S.

How you measure your milk, or your fuel or count your potatoes is trivial. But changing the rules is anything but trivial. That's why it is smart for us to let sleeping dogs lie. Besides, it ain't like we have 20 or 50 millions--we are a huge country with 300 millions. We are a big market. If people want to sell to us and we want it in gallons, by god, they'll find a way to sell it to us :-)

US engineers put a man on the moon 41 years ago. We must be doing something right.


Getting them there was "easy." It was the getting home in one piece that really was the wow! part.

During hard times, when cooperation and international funds would be a godsend, this can also turn into a disadvantage.

And "If the [Constellation] program is cancelled, 'zero' is the same in English and metric,".

Greetings,
Massimo


Till you look at the costs of R&D pure metric solutions from scratch, which would probably not be done so you'd end up with many 6.35mm, 25.4mm etc dimensions.

Dimitri


That article is superficial and doesn't address how these things work in practice.

In fact, why would you redesign the whole system just to be "metric?" You wouldn't. Rather, you'd make hard conversions within tolerances for some parts, and direct soft conversions for others, with a tolerance matching the existing but specified in the new units.

The interfacing parts could be designed in metric units, while the bulk of the legacy platform would, as you say, have "25.4mm" parts labeled as such.

There would not be any reason to convert all of the design drawings. Political and non-scientific people love to make a lot of hay about this metric "disaster" of the Mars thing. In fact it wasn't a "metric" issue as much as it was poor documentation. Assuming kilograms when grams or tonnes is improperly labeled, or cm vs mm, is just as much of a problem.

In the 1970s we "mated" with the Russians in space. I think we can handle it :-)


Quote:
In fact it wasn't a "metric" issue as much as it was poor documentation.

Yep, either not written correctly or not read correctly. But it's just sooo much easier to blame a system...

Quote:
Assuming kilograms when grams or tonnes is improperly labeled, or cm vs mm, is just as much of a problem.

Or... just plain getting it wrong: integrating an electronic box some years ago I noticed it had an error in the speed. I determined that the supplier had multiplied going from knots to m/s rather than divided. this may seem an imperial to metric conversion error at first glance, but the factor used was correct but the maths was wrong - they could have made the same error going from km/h to m/s or even just from km to m.

Yep.

"That damn Imperial system. Screws it all up!" ;-)

Edited: 8 Feb 2010, 11:23 p.m.

All looks nice and tidy, but in reality it gets messy. 1 calorie per degree c per gram for water. Oh, wait, the joule relates to the volt and the watt. Damn, I have some number other than 10 to convert with....

Oh well, so much for "perfect alignment of the heavens."


Hi Bill,

Quote:
1 calorie per degree c per gram for water. Oh, wait, the joule relates to the volt and the watt. Damn, I have some number other than 10 to convert with....

d:-) (emphasis added)

Mother nature doesn't care about human systems. But humans strive for optimum, so they started developing a system minimizing the need for memorizing strange numbers some 200 years ago. Of course, whoever feels brains shall be put in (converting) pints, may do so ad libitum - please see here d:-).

Edited: 8 Feb 2010, 5:08 p.m.

Calorie isn't an SI unit, so I don't see any problem.


Right, it isn't SI--but it *is* metric, and it correlates to water so nicely, which the Joule does not, yet the Celsius units do...and so it is another case where you can see "metric" being arbitrarily inconsistent--no unit system is perfect. Metric is great, use it all the time, but it ain't the end-all be-all that some would have us believe.

Another unit which is metric but not SI is the liter. *Gasp in horror*. "What! Yes it is! Yes it is! Frenchmen use it! It must be!" (No, it's not...sorry.)

Edited: 9 Feb 2010, 11:28 a.m.


IMHO, what we compare is SI and anything else, and the recommendation is to take SI. It may be called "go metric" in the US of A, but then "metric" is just another word for SI.

With that said, there were (and are) of course predecessors of SI, too. Way back, our forefathers used cubits (Ellen) and spans (?) and other strange measures like different miles. These were dropped in the process of nationbuilding and later to facilitate trade. Some names survived like in our pound equalling 500g. And there are some (actually very few) handy non-SI units for household use like the liter being exactly 10^-3 m^3, or the Zentner (= 50kg). You will notice, however, *very* simple conversions to SI there. So in real life, though only a minority knows it's called SI, everybody here moves smoothly within this system.

The Calorie is a relict of an older set of units. Like many other "practical" units it turned out to be less than practical in science, so it was discarded by an international agreement some decades ago.

So, if the US of A wants to support international trade by making it easier, it's obvious what to do. If it's not done, however, that's a statement, too. Anyway, an error won't become any better by being kept d;-)

P.S.: Admittedly SI is far from perfection, but it's the most perfect system we know so far. If you have something better, stand up and show.

Edited: 9 Feb 2010, 5:33 p.m.


Hi Walter,

My point was that calorie and liter are both *metric* but not SI. Calories are great with thermodynamics. Joules are great with electricity. Oh well.

Metric is a larger sphere than SI. Metric includes MKS, cgs, calories, liters etc that are not strictly part of the "systeme."

Also, American business uses a lot more metric than the rest of the world seems to realize. I've worked on a lot of projects that were metric. In terms of total number, maybe 30% of them. I've worked on projects that were 100% metricated from engineering to shop level, and on others that were engineered in mm and shop in inches(stupid but it works if done right). One job had a special scale made up to read a metric drawing in feet inches (now that's really being a foot-dragger!). American firms export lots of equipment around the world. Some of it was designed in feet / pounds, but a lot is also metricated. Our federal highway administration has been doing its roadway engineering in metric since the 1970s. Roads are labeled in miles (why change? We all know what a mile feels like. There is no need to relate it to your height, or the length of your boat or whatever...).

Where there is money to be made, business goes--and so if metric is specified, business complies. Vive la free-market!

The "metric pound" of 500g is more confusion actually (rather than 454g). Leave a pound a pound and it is better...but yes these things happen.

Edited: 9 Feb 2010, 7:13 p.m.


Hi Bill,

as written earlier already, I see the miles as you do.

For our pound (Pfund), it's just an handy unit people use at the grocers etc. - bad luck you use the translation in English. Both have a long tradition, almost no confusion in real life observed.

Referring to your understanding of "metric": You don't have to repeat all errors and detours the rest of the world made on its way to SI. No problems with liters etc. being just nice names for units fitting perfectly into SI. But please leave the calories and their siblings were they are: in the dustbin of history.

HTH,

Walter


We "metricians" aren't free from detours: In plumming almost all measures are in "Zoll" (inches). And the diameter of my bike's wheels is much easier remembered in Zoll than in mm.

What I'll never get into my head is "miles per gallon": We deal with "liters per kilometer" which is reciprocal to the imperial way of thinking. You answer the question "How far will I get with the contents of my fuel tank?" while we ask "What will it cost me to get to my destination?" Different question - different answer.

Edited: 10 Feb 2010, 8:49 a.m.


Hi Marcus,

We actually do use gallons per mile too--but not for little tiny cars. We use that for big machines (ships, trains etc).

Sort of reminds me of the choice of wave number or frequency...

That's funny about bicycle wheels. Here, we used to talk about 20" 24" 26" (three types: schwinn, raleigh, and balloon) 27" and 28".

But then with road racing, we started to use the European designations 700c, which ultimately supplanted the 27". At first, we would have 27" clincher training wheelsets and tubular race sets, and it would be a pain, having to slightly adjust the brake shoes. With 700c they matched the tubulars.

Ultimately, if you were in the business (rather than an ordinary Joe on the street) the metric rim diameter became the only proper way to do businees. 700c=622, 27"=630, 28"=635. These rim diameters are molded into the sidewall of all tires. Similarly, this would eliminate the chance for confusion between Schwinn 26" and standard (Raleigh) 26"....

So ironically, in the US, except for some overall sizing for marketing (17" frame, 26" wheels), we've gone completely metric. I along time ago switched from thinking about 23" to 24" frames to thinking about 58 to 60cm. Crankarms: 172,5mm, handlebars: Cinelli model 66-42(42cm), seatpost: Campagnolo 27,2 etc. Of course chain will always be 1/2" x (? or ? depending on track or road) and pedal threads will always be 9/16" because that is that....


Edited: 10 Feb 2010, 10:57 a.m.

Quote:
What I'll never get into my head is "miles per gallon": We deal with "liters per kilometer" which is reciprocal to the imperial way of thinking.

Just another way to look at it, take for example a trip from Toronto to Barrie is 60mi/100km. My truck burns 15mi/gal or 15.5l/100km.

That's 60mi/15gal=4 gal or 15.20$

While its in SI

.155klx100km = 15.5l and the same cost.

Yes I chose those 2 cities for conivance but the same applies for any distance.

Dimitri

Quote:
What I'll never get into my head is "miles per gallon": We deal with "liters per kilometer" which is reciprocal to the imperial way of thinking.

Ha ha, and I'm used to thinking in km per liter :). I also buy my car tyres as 15" by 195mm. Talk about a mix! :)

Tyres here in the US are normally designated in mixed units:

205/70R16

205 means 205mm wide, 70 is the aspect ratio (dimensionless) and 16 is the diameter in inches. There are "millimetric" diameter tires in which case you'll see something like 205/70R415 etc but these are uncommon.

Edited: 12 Feb 2010, 11:03 a.m.


Same here in Germany.


At least tires are consistently internationally mixed up....

I've to correct myself: It's actually liters per 100 km. It's a measure that leads to "easy" numbers in the range from 3 to 30 (depending on your car...)

Speaking of calories, does European food packaging list energy content in kcal or J?


For the time being, it's stated like "435 kJ (103 kcal)". AFAIK you may omit the Calories, at least you must not print them in a larger font than the Joules. Old customs die hard d:-/

@Dimitri:

FYI, "kl" is neither SI nor conventional nor used. Since 1000 l = 1 m^3 , it's redundant. You're young enough for learning d;-)


Quote:
@Dimitri:

FYI, "kl" is neither SI nor conventional nor used. Since 1000 l = 1 m^3 , it's redundant. You're young enough for learning d;-)

Yes I realize that now thanks. Always avoided powers that made the equation look large. That is what I was taught in school, 1km not 1000m or 1x10^3m. Similar to why I have always used asin/acos/atan instead of the power to the negative 1.

Dimitri

Quote:
How about the so-called "Gimli glider," an Air Canada jet that ran
out of fuel and nearly crash-landed but for the skill of the pilots, due (in part) to confusion between US and Imperial gallons.

umm, no. As this NewYork Times article title clearly states its was a metric conversion error:

JET'S FUEL RAN OUT AFTER METRIC CONVERSION ERRORS

By RICHARD WITKIN (The New York Times)

July 30, 1983

"The carrier said that fuel had been measured manually with special ''drip sticks'' because the electronic gauging system aboard the plane, Air Canada's first metric aircraft, was not working properly. But in converting the fuel volume determined from the stick readings into total fuel weight, the wrong conversion factors were used. The net result was that the pilots apparently thought the figure for fuel weight on board was in kilograms when it was really pounds. Since one kilogram equals 2.2 pounds, the plane took off with about half the fuel that it should have had."


Quote:
As this NewYork Times article...

You actually believe anything the press has to say? (I'm a bit pessimistic about the press, taking news items with a grain of salt*)

Referring to Geoff Quickfall's (an airline pilot in Canada) good description of the probable sequence of events (elsewhere in the thread), it indeed seems conversion problems had a role to play. But, I would put the ultimate blame on the procedures of the day, i.e. allowing a commercial passenger aircraft to take off without operative on-board fuel indication. Perhaps this came from an old view of "that's how we did it in the old days anyway" (referring to the assumed adequacy of drip sticks).

However, with high volume air travel requiring ground personnel to service many aricraft per day and airlaines demanding shorter turn around times, the amount of conversions to and fro (volume to weight conversions, different unit conversions), i.e. increased ground personnel & aircrew work load, old procedures may not be adequate. Unfortunately it takes these kind of incidents (and many with more tragic consequences) to highlight and change inadequate procedures (the last point 4 in Geoff's post).


*From my Dutch backgroud: "take with a grain of salt" is to not take too seriously/literally

Sorry for "shooting from the hip" without remembering the details
of the Gimli glider story, I just wanted to get it out for some
responses. Wow, thanks to Geoff and the other professionals out there for the quick crash course on aviation procedures. I am an
airplane buff and only got my student ticket way back, but love to hear about how things are handled behind the scenes (YouTube has
helped in this, with all their cockpit videos - the best has been the Virgin Atlantic 4-part series). Also interesting is the use of
HP's to verify the "great circle route" parameters. That is a heck of a calculation (derivation, actually) in itself. Again, thanks to all -- Glenn

The questions of fractions and SI units are old ones (at least relatively).

If you have nothing better to do you can look at this thread from a model rocketry group :

SI Units in Science Thread

It is only 96 posts long so maybe a little short by the standards here <vbg>.


Even within one country, unit confusion can cause problems.

During WWII, the British decided to fly some Spitfires off a carrier to the island of Malta. Because of U-boats and Luftwaffe bombers, the Navy wasn't too keen on sailing one of their big carriers in the confines of the Med, so they asked the Air Force how close they needed to get. The RAF replied "xxx miles." The RN said "Righto" and dropped them off xxx nautical miles from the island.

Amazingly, four of the twelve Spits made it.


That's only 15% difference. Shouldn't matter so much, unless you plan your missions to the last drop of fuel....

Quote:
During WWII, the British decided to fly some Spitfires off a carrier to the island of Malta. Because of U-boats and Luftwaffe bombers, the Navy wasn't too keen on sailing one of their big carriers in the confines of the Med, so they asked the Air Force how close they needed to get. The RAF replied "xxx miles." The RN said "Righto" and dropped them off xxx nautical miles from the island.

Amazingly, four of the twelve Spits made it.


There is a fairly long discussion of the several missions to supply Spitfires to Malta with British aircraft carriers and with the American carrier Wasp in Wikpedia but there is no mention of the incident that you describe. Would you please provide a reference for this story?

Aviation flight planning these days is done pretty much exclusively in nautical miles, knots, etc. (the exception being the old Soviet Union, which was metric to the extent of even having altimeters calibrated in metres). I've never worked any other way.

However, I went back and checked in my father-in-law's navigation textbook, which he used when training as an RAF navigator in 1944 (he flew in night fighter Mosquitos, towards the end of WW II). Although it mentions statute miles, nautical miles and kilometres when introducing measurement of distance, all the calculations after that are done in nautical miles and knots.

But then I pulled my copy of "Air Publication 1565E and Air Publication 2280 A, B & C - Pilot's Notes - Spitfire VA, VB and VC Aircraft and SeaFire IB, IIC and III Aircraft" (1943) off the shelf. It quotes speeds for cruise, stall, aerobatics, etc. in m.p.h. EXCEPT in the Addendum for the Seafire, where the notes on "Deck landing" quote speeds in knots.

(On the other hand, my "Pilot's Notes" books for the Mosquito - which date from 1949 - give all speeds in knots.)

So, it's possible that the RAF was still working in m.p.h at that time while the Royal Navy used knots. I'd be surprised if they made such a fundamental flight planning error, though.

Best,

--- Les

[http://www.lesbell.com.au]


I couldn't verify the Spitfire story but I did find a very similar story about sending Hurricanes to Malta from the H.M.S. Argus on November 17, 1940.

Here's an idea on what went wrong: Models of the Hurricanes revised for flight from aircraft carriers appeared later in the war but were not available in 1940 so far as I have been able to tell. The Hurricanes flown from the H.M.S. Argus had been designed for flight from land. Could they have taken off with less than full tanks to reduce the distance to take-off to that available on the carrier.

One of the interesting things that I discovered during my reading was that the pilots who flew Hurricanes did not have a high regard for the Spitfires, and vice versa. That was reminiscent of the mutual disregard of other machines by the pilots of F-100's and F-101's in the late 1950's. And, of course, that is similar to the mutual disregard of the TI and HP communities for the other company's machines.

What was the size of Bill Hewett's shirt pockets


I don't know, but I'm pretty sure that it was neither 7.24 x 3.47 x 0.98 cm nor 18.4 x 8.8 x 2.5 in.


Really? I always thought he was wearing one of these :)


d:-D Looks like tailored in North Korea ;-)


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