You know that Global Positioning (GPS) wouldn’t be possible without accurate clocks. So each GPS satellite is equipped with very accurate atomic clock which absolute accuracy is ±1 second over 1 million years. Having such precision you wouldn’t have to adjust clock settings in all your lifetime. Practically if you have a GPS receiver you already have a accurate clock. Darius had and Arduino and Sirf II GPS module around and decided to make clock with time and date display.
Originally GPS receiver communicates using RS232 interface. So in order to connect to Arduino there is a UART to RS232 level converter needed like MAX232. Sirf II GPS receiver sends data using NMEA protocol which is based on sending ASCII messages. To make things a bit interesting Darius also displays some additional information on LCD including number of satellites and GPS fix that indicates GPS module RTSS synchronization.