Maybe this is the best Arduino RTC module. This RTC module used the DS1307ZN+ IC, to make this RTC module really reliable and stable, it works from -40℃ to +85℃, completely solved the problem of not working when cold or hot that most of the other Arduino RTC module encountered.     It uses the I2C protocol to communicate with Arduino mainboard. You can download the Starter Kit Guidebook experiment 08- Get Real Time Clock and related source code to learn how to use this module.