Rotor-Racing manual lap-count buttons

These are the spotter buttons I used at Weston Park Dronefest 2017.

Many race control software packages (including the free Laps Free from RCTiming.com) allow you to use the number keys to simulate competitors crossing the finish line, or even to manually register missed laps should a competitor's transponder work unreliably.

They can be made very cheaply from readily available components and used where the cost of lap timing systems is prohibitively expensive.