!7bii+ vs other HP calcs


On my 17bii+ I put PI on the stack and multiply by 100 and then divide by 100. I put PI on the stack again and subtract. I get 2.1E-13. None of my other HP calcs do this--I get zero. Why?


Please explain to me how this is a useful calculation....

but it has to due with the internal significant digits the calculator maintains and round off errors during calculations in the least significant digits....


Sheesh, even my 1973-vintage TI SR-20 desktop scientific gives an answer of zero for pi*100/100-pi.

Maybe you should be happy to have a pi key on a financial calculator at all. :) Doing a quick survey here, none of the other HP financials that I have contain a pi key.


OK, It does it even if I multiply PI by 1 and then put PI in the stack and subtract. It shouldn't do it. It should be just zero. I don't know why or how I stumbled on it, but it just seems odd to me. The other calculators (11c, 48GX) don't do it. The 17bii+ gives a non zero number (2.1E-13), and I don't care whether it's a financial calculator or not--it shouldn't do it.


I have no idea what the internal architecture of the 17bii+ is, but I'd be willing to bet that the error is due to the calculator doing some unnecessary BCD-to-binary conversions.

On hp's web site, the calculator is listed as having "memory capacity unlimited within available memory." What the hell is that supposed to mean?

Maybe they should also state that accuracy is "unlimited within available significant digits." ;)


My 17BII gives 0 like the other "old" HP calcs. Does the bii+ use the BII ROM in hardware emulation?



I guess the trouble is caused by improper binary
to decimal conversions and back in the emulator. Older HP calcs
did use BCD, which allows for exact representation of
base-10, decimal quantities such as 0.1, while 0.1 is a periodic,
never-ending fraction in binary (base-2).

As a simple test, just try to calculate Pi*1-Pi in
your trusty Windows XP standard calculator applet (Scientific mode).
You should get a 0, but actually you get instead:

  [Pi] [*] [1] [-] [Pi] [=] 

-> 3,1370505526082969463696315942562e-38

Close, but no cigar ! Pi + 0 - Pi gives the same result.

Best regards from V.

Edited: 24 Nov 2003, 9:26 a.m.


Well, I infer from this that either there is a stupid bug in the low-level routines that emulate the BCD-type arithmetic operations done in hardware on the older machines, or HP have finally decided that binary floating point is good enough for financial calculators (and maybe even for all of them -- has this been tried on the 49G+?).

Personally, I'm hoping it's a bug, and not a policy change, since the latter would indicate that HP had misplaced their understanding of the need for consistency of operation. Which would be sad.



my favorite test is the next:

3 [ENTER] [y^x] 27 [-]

And the test for PI:

355 [ENTER] 113 [/] [PI] [-]



I'm not biting.


The operations 355 / 113 gives an good approximation for Pi that typically has the following error:

(355 / 113 - pi) / pi * 1E+09 = 84.xxx



Another test would be :

355 [Enter] 113 / [Enter] SIN + SIN

Which is quite close to zero. 48GX gives -2.06E-13, a nice PC1262 could probably do better as the result obtained from Maple (for instance) is about -3.16E-21.


Hi Brent!

Just wondering; what are your thoughts of the 17BII+? Is the keyboard the same as the 10BII, or is it better quality than that?

Now that the 17BII+ is out, I find the ebay prices for 17BIIs has dropped; would you suggest that I get a backup 17BII while I can, or should I pick up a +?



I only have a 12c so I can't tell you anything about the other business calcs. It seems like a pretty good calculator but it has kind of a hollow or tinny feel to it. The eqation SOLVE part is nice. I wish they would make the 33s equation solver the same way. You can use names for variables and input values via softkeys. The 33s will only allow you to use A thru Z for variables (I think). I would go ahead and get the 17bii+ if I were you. It works fine, but it just doesn't have that feeling that you are holding a valuable piece of equipment.

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