Add a "Begin warm-up" button

I'm still having trouble with interpreting the first screen, where it says Warm up reps & weight. I hit "Begin Exercise" then it says 3 sets of "x" weight. (Prior screen gives rest interval of 50 secs). So I just do the 3 sets, keeping an eye on the time myself. This is where I think there should be a "Begin warm up" button at this screen. It would then initiate the timer clock. 

You would do the 3 warm up sets and begin the actual exercise.

Thx

Derek