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ESP_igrr wrote:Internal RTC clock frequency error is about 5%. With external 32k XTAL the error will be determined by the XTAL, usually about 20-30ppm.
The de facto standard in the industry for crystal inaccuracy is 20 PPM
You can also express PPM as a percentage: ±20/1,000,000 = ±0.002%. So after 30 days (2,592,000 seconds) we can expect the clock to drift about ±52 seconds; after 60 days about ±104 seconds, and so on.
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