Being a successful putter means consistently marrying line and speed. But in order to do that, you need to be able to see the different lines that the ball can possibly take as it rolls across the green. There’s a “high” side and a “low” side to every putt, and if you can’t see the difference between those, you’re limiting your ability to read greens.
This drill helps develop that feel and imagination.
Pick a putt between 10-20 feet with some break in it, and practice finding the highest and lowest break points possible to still have the ball go in the hole. This will mean altering speeds in the process. Developing your imagination will help you better manage your line and speed on the greens.