It works pretty well, but it assumes the green speed is consistent. Remember Muirfield? Down here, we putt on a lot of bermuda grass and the greens aren't nearly as consistent as bent grass due to grain, what treatment is being done, the humidity and a lot of other factors. In a sense, if you can work on your speed control such that you consistently roll a 10 foot putt 10" or 12" past the hole and find the line from you ball that would give you a dead straight putt (the zero line) and aim a bit away from that line to the side the cup is on, you will make a lot of putts. In other words, practice putting for 20 minutes as often as you can.