[bhouston]

Clocks do drift. Seconds a week is definitely possible. I think there are varying quality of internal clocks in electronic devices, and the cheaper the quality the more drift there is. I think small cheap microcontrollers can drift seconds per day.

[ycui1986]

cheap microcontrollers use RC oscillators. If they only drift a few seconds a day, that would be an achievement by itself.

RC oscillator is poor enough that early days USB communication would fail if running on RC clock.