Displaying the Current Frame in the movie

I am working on a simple test for hand/eye coordination, and I would like to have the current frame displayed in my movie, some people have to press the spacebar when 2 things line up, and they line up exactly on frame 49. I want it so when the people press the spacebar, it says what frame they are on (since its at 100 fps), they can then see how many hundreths of a second they were off.

Does anyone know of a simple way to just display the current frame in the movie, so that when they press spacebar, they can see how many frames before or after there were from the target?

Thanks alot!