Be careful about going back too slowly though. If you take too long setting your power in your backswing, your forgiveness suffers. Draw the putter back slow to 50% and notice how the forgiveness bars decrease and then stop moving once you hit 50%. Continue to hold the putter at 50% and watch how it starts to shrink again because you're holding it too long. All clubs on all shot types do the same thing.
My recommendation is to bring the meter out to the power you want and mark it with your eyes or put your finger on the screen. Remember that the time it took you to find where you wanted your power is counting against your accuracy should you mishit. Swing through the first time (or just unwind) and then quickly take a rip at it for the best (and most accurate) results.