HP-28S Clock Accuracy



#9

Although it is not mentioned in the manual, it is possible to set up a clock in the HP-28S using a set of programs.

A while ago I got two 28S and loaded the programs. I do not use a watch, and I always find out what time is it with a check on one of my calculators or PDAs.

Because of some unfortunate events I had to put both 28S in storage two years ago, with batteries. Last weekend I got them out of storage and checked them. Fortunately, the batteries did not leak and the battery compartment was intact. Then I checked the clock. It was fifteen minutes past the current time on one of the calculators, and fourteen minutes before on the other. Other than this, the two 28S were fine and now have new batteries.

I have checked about the accuracy of the program on the documentation I have but there is not much. Does anybody have any experience on this?

Thanks in advance.


#10

I am surprised that you would be concerned about it. An error of 15 minutes in 2 years is only 28 parts per million, which is well within spec for an untrimmed 32 KHz crystal oscillator such as the one in an HP-28S. Few pieces of consumer electronics can achieve any better, aside from devices which depend on an external frequency source such as GPS, time broadcast by radio, or power line frequency. Certainly PDAs rarely have better timing accuracy.

Assuming that the storage was not temperature controlled, that's actually quite good. A wristwatch can do better (while on your wrist) only because it is operating at a much more stable temperature than it would in free air.

When you also consider that neither the HP-28C nor the HP-28S were specifically design with timekeeping in mind, and that the documentation on how to access the internal clock was only released as an afterthought, I think you should be quite happy with how well they work.

Eric


#11

Hello Eric,

Thank you for your explanation.

Quote:
When you also consider that neither the HP-28C nor the HP-28S were specifically design with timekeeping in mind, and that the documentation on how to access the internal clock was only released as an afterthought, I think you should be quite happy with how well they work.

Indeed I am happy with the clock application of the HP-28S. It is a testament to the quality of HP. My concern was rather curiosity on how well the clock performed, and it is impressive how well it does. I am amlso surprised by the battery life. According to the manual, alkaline batteries would last 180 days on an HP-41, and about the same time in an HP-28S. I have seen 41s going on the same battery set for three years of sustained use (not including the card reader) and now almost the same time for the 28S. An HP-48GII is expected to drain its batteries in two months, as per specifications; I have no idea of the figure for a 49G+ Again, HP did know how to build fine instruments.

I remember I was concerned about the hinge contacts of the Clamshells when I got the first 28S. Time has proved me wrong.


Quote:
Assuming that the storage was not temperature controlled, that's actually quite good.

Yes, they were stored in a friend's warehouse without temperature control.

The 28S is powerful and handy when you get used to the keyboard layout. No Alpha toggle to deal with, just typing in the object name. I think it was conceived for use at a flat surface (like a desk or a table) only, and for quick calculations away from it (and folded as the manual suggests for "field use")

#12

This is slightly off topic, but I now wonder about the precision of the clocks in the HP 48G's and HP 49G+.


#13

I ported my UAC to my 48GX and the clock proves useless. Indeed, there is a program to correct this: Adjustment program for the 48 clock.


#14

For the HP-49G/G+, I would suggest Prof. Dr. Wolfgang Rautenberg's
Timeman (Timeman.zip).


#15

To Messrs. Isene and Barbosa, thank you very much for pointing out to me these programs! I remember going through 48G and 49G+ files, but there are actually so many. Believe it or not, there are few times I actually have had to depend on my 48G/G+ for timekeeping... thank God it wasn't too critical an application.

#16

Fifteen minutes over two years is well within the frequency tolerance that can be expected from ordinary quartz crystal oscillators.


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