To enable the Count Down feature: Set the desired time and press START/STOP. The alarm will sound when minutes and seconds count down to 0. To enable the Count Up feature: Press START/STOP to count up to 99 minutes and 59 seconds. Each digital timer has a magnetic backing to use on most flat steel surfaces; ideal on metal whiteboards. Each set contains 3 Nexus LCD Digital Timers (yellow, blue & green).