I wanted to test out how accurate timing in vanilla Scratch is... Obviously there may be a better way of doing this, but I figured I'd try this time around with the 'days since 2000' block. Simply press your 'S' key to the beat and monitor your results. Please write a comment with your findings! You can also tweak the settings above the meter; there's more info in the notes.
Framecomp (How much offset is applied to your inputs): A: None B: Half a frame's worth C: Whole frame's worth Sound (What you hear while monitoring): A: Nothing B: Metronome only C: Metronome + music