The Arc Glider Golf Putting Aid
The best way to ensure your putter face is truly perpendicular to the arc board you are using is to extend the flat surface area on the heel of the putter.
The Arc Glider was designed by the makers of the Putting Arcs (model "Deluxe, HD, MSIII and T3) to hold the putter in place perticularly for anyone struggling with rolling the hands or trying to guide the head too much vs. letting arms, shoulders and back guide the putter. Any face rotation is difficult and will immediately be noticed.
Fits virtually all putters with adhesive tape or a rubber band.