The Extech STW515-NIST Stopwatch and Clock with Backlit Display is a digital stopwatch and clock. This stopwatch features a 12 or 24 hour clock format and programmable alarm with hourly chime. It also has three Stopwatch Modes: Elapsed Timer, Split Time, and Two Competitor Timer. The backlight can be used for viewing at night or in dimly lit areas and turns off automatically after five seconds. The calendar displays day, month, and weekday. It includes NIST Certification.