Rpm test in flight videos with Android phones

Just noted that my Android phone is capable of showing the screen split between 2 applications running simultaneously..so I ran on the bottom of the screen one of my youtube vids shot on my Toucan RC plane powered by my oldest TD051 with a keychain cam fixed on the wing, while also switching on an acoustical rpm sensor app on my phone on the upper half of the screen that measured the engine rpm audible from the lower screen half, and made this screenshot by swiping my hand over the screen:



Quite funny way of documenting engine unloaded speed..