This is a digital RTC - Real Time Clock and an EEPROM made specifically to be used with the Arduino, Raspberry Pi and all other general purpose microcontroller which supports I2C interface. The RTC can be used to store and retrice the current time, while the EEPROM offer 32 kb of storage space which can be used for data logging. The RTC will use its inbuilt battery to keep time even when the Arduino, or the external microcontroller is powered off. Similarly the EEPROM saves its data even after a power off. This makes this module perfect for timekeeps and datalogging.
The module uses the DS3231 IC for timekeeping. The DS3231 is a low-cost, extremely accurate I2C real-time clock (RTC), with an integrated temperature-compensated crystal oscillator (TCXO) and crystal. It maintains time as seconds, minutes, hours, day, date, month, and year information. When there are less than 31 days of the month, the date will be automatically adjusted, including corrections for leap year. The clock operates in either the 24 hours or 12 hours with AM and PM indications. The RTC works on external power when available and whichs to use the onboard battery powower supply when the external power supply is turned off.
The DS3231 is one of the best RTC available and offers the highest accuracy with least power consumption. It can keep time using a single Cr2302 battery for years with least variation.
Since this is a very popular board, Arduno libraries, sample codes, example projects and tutorials are avaiable on the internet.