can you use this to work out how fast the diabolos are spinning?

be a lot less complicated to just put a little mark on the rim of the diabolo. take, lets say 4 seconds of footage. slow it down, count how many times the mark goes round in that time and then just use speed = distance/time. using the circumference*the amount of times the diabolo revolves....

Wow - Can you do my Math degree whilst i play with my diabolo? Thanks.

True, but what is "time" in your formula? 4 seconds? I think not. Doing what you do gives you relative speed. not the real speed

Thats what I was getting at, and then because we know how slowed down the footage is we can multiply it back to normal speed. would this not work?

I was asking whether you could use this camera to work out the speed of the diabolo, not just this video.Supposing you had a mark on the diabolo, you slowed down the video, counted how long it took the diabolo to spin say 10 times and then worked out by how long you slowed the video down by then you could work out how fast it was spinning.