Adafruit DS3231 Precision RTC Breakout
This Real Time Clock (RTC) is the most precise you can get in a small, low power package. DS3231 has the 32kHz timing crystal inside the chip and right next to the integrated crystal is a temperature sensor which compensates for the frequency changes by adding or removing clock ticks so that the timekeeping stays on schedule. Great for datalogging and clocks, or anything where you need to really know the time.
Your Price: €18.27
Weight: 5 g