Adafruit ds3231 precision rtc real time clock breakout boards adafruit 3013 p the adafruit ds3231 precision rtc real time clock breakout boards are cleverly designed to compensate for thermal drift making them some of the most accurate rtcs available in a small package the timing crystal is inside the chip and there s a temperature sensor right next to it so that clock ticks can be added and removed to maintain accuracy a simple cr1220 coin cell can keep the clock ticking for years the ba