The ChronoDot RTC is an extremely accurate real time clock module, based on the DS3231 temperature compensated RTC (TCXO).
The ChronoDot was one of the first handy, easy-to-use "RTC" (real time clock) modules. It's based on the DS3231 temperature compensated RTC by Maxim semiconductor. It includes a CR2016 battery which should last at least 8 years if the I2C interface is only used while the device has 5V power available. No external crystal or tuning capacitors are required.
The DS3231 has an internal crystal and a switched bank of tuning capacitors. The temperature of the crystal is continuously monitored, and the capacitors are adjusted to maintain a stable frequency. Other RTC solutions may drift minutes per month, especially in extreme temperature ranges, where the ChronoDot will drift less than a minute per year. This makes the ChronoDot very well suited for time critical applications that cannot be regularly synchronized to an external clock. Here is a live demo of a DS3231 chip that has been keeping time since it was last synchronized in 2005: DS3231 Web Demo
The ChronoDot will plug into a standard solderless breadboard and also has mounting holes for chassis installation, and is ideal for using with a "EMSL Bulb-Dial" clock.
The I2C interface is very straightforward and virtually identical to the register addresses of the popular DS1337 and DS1307 RTCs, which means that existing code for the Arduino, Basic Stamp, Cubloc, and other controllers should work with no modification.