...I'm a little nonplussed by your experience with declining accuracy. That should be un-possible. But anything that happens must be possible. There was a design change part way through the production run, with early units running a 4 MHz clock instead of 12 MHz. My unit was a later unit. Wonder what else they changed, and if that had any effect?
I wonder if damage to a circuit board or other component would account for the declining accuracy? The reason I asked about damaged equipment earlier is because my experience has shown that unserviceabilities like cracks or impacts from rough handling do not always stop something from functioning, but will degrade performance. Muzzle blast, heat from the sun or improper handling may cause problems.
When I was in the military, I had to get regular physicals as part of my overseas duty. The medical people had a new fangled blood pressure gauge that automatically inflated and took readings. I was almost removed from duty because my pressure was recorded as being 200/95 on several tries. I asked if these BP units were properly calibrated. I was rudely told that they "self calibrate" and cannot give bad readings. Ah...
At my insistence, the doctor used an old fashioned BP gauge with a manual bulb inflator. Strangely, using the old school BP gauge, my reading was 116/74. As a technician, I know that calibration is a process of verifying and, if necessary, adjusting a piece of equipment to ensure it is operating within its design parameters. Sometimes, things can go wrong, but not disable equipment completely.
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