The Putt Ruler, designed by Bob Walton. In teaching putting, historically I have taught players first how to practice by making 10 putts in a row from 2ft,3ft,4ft, etc. Straight putts, curves,uphill and downhill. If we need to go to the mechanics we do.
The Putt Ruler teaches people how to read breaking putts as well as alignment,path, and what it feels like to compress your putts. It is the best putting aide I have ever worked with!