If you use the pre-printed range strips you have to zero at 20 yards and then shoot at 60 yards to determine which strip to select.
That said, once zeroed you can then set the crossbow to any range you want and simply hold over or under if that's your liking.
After running the ballistics on the Tac15
I discovered that you can set it to 25 yards and be pretty good at ranges from 5 to 32 yards. Good enough for shooting deer, that is.
Jon has a technique for using the Optimizer that does not involve the strips, but you need to tabulate and print out what yardage corresponds to what mark on the 'bare' dial. The instructions for doing this are on this forum somwhere.
If your crossbow scope runs out of adjustment before zeroing at 20 yards you'll have to shim one of the scope rings. The newer HHA Optimizers don't need shimming. My understanding is that you need a shim with the older ones.