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Jun 24, 2017, 01:19 AM
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Trimming Heroineclock II


So Heroineclock II's mane problems were it had an offset crystal & it was calibrated from a computer RTC which itself was offset. It gained 5 minutes over 77 days. Its internal clock increments 250 times per second. Thus, it needed to subtract 5 * 60 * 250 ticks every 77 * 24 * 60 * 60 * 250 ticks or 1 tick every 22176 ticks.

Unfortunately, it had an existing trim factor of adding 1 tick every 10300 ticks, so the 2 trim factors need to be combined. The trick was to multiply 22176 * 10300. This predicts the existing trim factor adds 22176 ticks for every 22176 * 10300 ticks & the new trim factor subtracts 10300 ticks for every 22176 * 10300 ticks. Thus, the total change in ticks every 22176 * 10300 ticks would have to be 11876 or the addition of 1 tick every 19233 ticks. The new addition is less frequent than the old addition, so it satisfies the need to slow the clock down.

We still need to reduce the 19233 to 19230 make sure the clock doesn't run slow.
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