This is a smallest Real Time Clock (RTC) Module based on DS1307 chip by Maxim. This small RTC module comes pre assambled with CR2032 battary socket, This tiny button cell can last for 10 Years typicaly. DS1307 RTC is accessed by IIC protocal and pul-up resistors are provided for IIC lines. RTC module is suitable to keep track of Year, Month, Day and time.
For more details on this RTC module see the manual of this module.