Not sure how many use it, or maybe those that have done it won't say, or figured it out something to use for it.
On the green once you are ready to start putting, something I have used in all 5 golf games I have played. Instead of guessing "How hard to hit a good putt " or watching for this or looking to see this. Simple to do, something everybody has, takes 2 things.
1. a piece of paper.
2. something to mark with.
Go to the putter so you can select different settings i.e. 15 / 30 / 50 / 100 or what ever your selection are for the putter you use.
Take the edge of the paper lay it so you can see the start and full power.
Mark the 2 places where it starts and full swing
Fold the paper so those 2 marks line up on each other that is half power mark it there
Fold again to line up the next edge to give you 1/4 and 3/4 power
when finished you will now have a scale to go by, if you set it to lowest setting you should have marks for the range in feet / as example if you had a putter that 25 was lowest marks would be / 0, 3 feet, 6 feet, 9 feet, 12 feet, 15 feet, 18 feet, 21 feet, and full power 25 feet.
Use all 4 edges in same way you will have a scale for every type of putt just about, with less wondering and guessing. Helping you to putt with more confidence to lower those scores. Used this to sink a 60 foot putt today with the Spider Putter, up hill against a break away green slope.