Ten Seconds, Ten Pulses. Click the screen or hit space when the pulse is at it's minimum. The closer you are to the minimum, the better the score. Try to get the lowest total score over all ten seconds.

Please let me know in the comments if you are having problems running a particular build, and please don't rate if that's the case.

[I added a restart button to the level end because, holy crap, refreshing is annoying.]