If you want to make your own electronic watch,a RTC module is necessaryto generate you the right time, with very low power consumption.
This tiny RTC module is based on the clock chip DS1307 which communicates with microcontrollers with I2C protocol. The clock/calendar provides seconds, minutes, hours, day, date,month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. Besies, this module is really low power consumption, it can serves you more than a month with a CR1220 or CR1225 battery.

Features

• Connection Mode: I(IIC)
• Low Power Consumption, High Precision
• Dimensions(mm):20.0(L)x20.0(W)x10.0(H)

Parts list

• 1 X Crowtail-RTC 
• 1 X Crowtail 4 Pin Cable

Links

• RTC Schematic
• RTC Program
• Wiki link