This device will measure and record your planes top speed. It comes with two pitot tubes and a hose and measures your planes speed in the same way as a normal plane does.
The HowFast unit will record your planes top speed and display it back to you in a series of flashes, once you land. If your plane travelled at 125MPH it will flash like so: * ** *****
Its super simple, doesnt require a PC and weighs only 2.7g

Spec.
Speed range: 15 to 500MPH (24-800kmh)
Resolution: 1MPH (1kmh)
Voltage: 3.2 ~ 12v
Size: 26.7 x 16.5 x 4mm
Weight: 2.7g