right, a rear free hub with a 10t sprocket and a 50t sprocket on the cranks would give a ratio of 10:50. Simplified this would give a 1:5 ratio. So for every 1 turn of the cranks the rear hub would turn 5 times. So lets say we had a 50 engagement hub. This would mean for every time you rotated the cranks once, you would get 250 engagement points (bit extream!). The 250 divided by 360 (one crank rotation) would give you the engagement points per degree. In front free wheel terms the engagements never change, nor do the engagements per degree because you are turning the freewheel directly.