HP48 Clock Variableness

[TomC]

Thank you all again for your contributions here.

Just some 'sidenotes' from me:

1. The experiment continues - I have a number of machines that all were synchronized (within a 'secondish') and started on Feb 14. I will gather some data perhaps in a week or so after the start time.

2. I've found that I have some 20ppm 32768 crystals in my stock.

3. I've found that 5ppm crystals are available at a reasonable cost (approx 0.63 USD).

4. A calculation shows that 11 days is about 1million seconds.
This means that a 20ppm crystal could be 'off' by 20 seconds in 11 days, or about 1 minute in 2 months.
-or-
a 5ppm crystal would be 'off' by 5 seconds in 11 days, or about 1 minute in 4 months.
(these calculations are 'rough' - you can check/detail at your convenience! ) This calculation is only based on the crystals frequency accuracy and does not account for frequency stability.

The bottom line is, I don't anticipate that it will be worth my effort to open up these machines to improve the performance to this level.

So, after my ongoing experiment, I will simply set some 'middle of the night' CLKADJ alarms. I may then setup a group time update - Establish a 'main machine', then IR its time to the other N machines.

[I do wonder what some devices used - I do recall VCRs back in the day (in the early 1980s - before the autoadjust feature) that were very accurate - within a minute over a year. I realize that later, the VCRs would 'autoadjust' and get time data from a local broadcaster.]
[I wonder if these VCRs used the powerline frequency - I have heard that this 60Hz source (here in the USA), is extremely accurate over long time periods.]

Cheers,
TomC