The Spektrum™ Lap Timer System is an extremely simple to use personal lap timing device that displays lap time information directly on your compatible Spektrum radio. The Spektrum Lap Timer receiver is less than one-inch square, weighs just 4.2 grams and works with the Spektrum Lap Timer Base Unit/s (SPMLTG5000 , sold separately) to send lap time information directly to your compatible Spektrum radio. With the Spektrum Lap Timer System, racers can upgrade their telemetry-equipped model to assist with race practice, use it for local competitions, or just play head-to-head against friends. All it needs is a small space on your model and a 4.0–8.4V power source