For excellent accuracy time-keeping - when your everyday RTC (Real Time Clock) won't do - the Adafruit RV-8803 Precision Real Time Clock Breakout Board is a tick-tock above the rest with excellent ±1.5 ppm (at 0~50°C) accuracy. Thanks to the built-in crystal with temperature compensation management, classic RTC drift is minimized so you don't have to do any time correction with WiFi or GPS to keep current. Compare it to the popular DS3231, with ±2 ppm (0~40°C), you get even tighter spec'd performance, at a better price!