The datasheet for the DS3231 explains that this part is an "Extremely Accurate I²C-Integrated RTC/TCXO/Crystal". And, hey, it does exactly what it says on the tin! This Real Time Clock (RTC) is the most precise you can get in a small, low power package. https://elecena.pl/product/17500990/adafruit-ds3231-precision-rtc-breakout 2021-04-06 https://elecena.pl/product/17500990/adafruit-ds3231-precision-rtc-breakout 2022-03-20