This is a great battery-backed real time clock (RTC) that allows your microcontroller project to keep track of time even if it is reprogrammed, or if the power is lost. Perfect for datalogging, clock-building, time stamping, timers and alarms, etc. Equipped with PCF8523 RTC - it can run from 3.3V or 5V power & logic Works great with our RTC library or with a (or similar single board linux computer) Note: This product does not come with a CR1220 coin cell battery. We recommend you purchase a coin cell battery to use with this product. Specification: Material: Plastic Size Chart: 20x20mm/0.79x0.79inch Package Includes: 1 PiecePCF8523 RTC Breakout Board Module Note: 1. Please allow slightly error due to manual measurement. 2. Due to the difference between different monitors, the picture may not reflect the actual color of the item. 3