When you look at the Drumming exercises, especially the Combination one, it may not look clear and you may want to speed the playback up or down.
Click on the Noteflight symbol on the bottom right and that will take to to the actual Noteflight page where it will display properly and you can adjust the tempo (speed) in the bottom left hand corner.
Cheers and happy drumming 
justin
Admin
Chris
justindwyer