(Script needed) fps counter

I can't find one of these on here so I have posted this in hopes to find someone good at scripting and has the time to mess with it.
What I'm needing is a simple feet per second counter that reads the exact amount of force on either side of the counter (.00 value not needed only whole numbers) . It needs to hold this value till it gets a new reading. Basically a smart target that can give me a number on how hard it was hit buy a flying object.
Design it any way you want, preferably keep it small and compact/movable and all together.