The Shaw slope gauge is a practice device used in golf, specifically putting to determine the percentage of grade between the ball and the hole. A player stands over the gauge centered on the device and then gets their body level to the slope holding the end of the putter 36″ off the ground. For every ⅜ of an inch the putter head moves is 1% grade. Once the player has this knowledge they then can apply the Simple green reading technology to determine the break.
On the gauge there are cutouts with different widths. The player will measure the shaft of their putter to determine where ⅜ inch is on the shaft. That is their measuring point. When they hold the putter out in front of them lining up the putter looking thru the spot at ⅜, the width of the shaft is ½ of a percent. So if one uses the gauge and it moves ¾ of an inch then they know it's a 2% grade. If the shaft is ½ then the area the shaft covers is doubled to get a one then times by 2 because it's a 2% grade and that gives them the read.
If the area the ⅜ section on the shaft covers is 4 inches by the hole, then a 1% is 8 inches times by 2 then their read would be 16 inches. Once the player gets the feel of how many inches the shaft is at different lengths of putts then it becomes simple.
The other cutouts on the gauge are to measure different spots on a putter or putter grip. If the top of a grip is 1½″ the player can hold the putter in front of the and look at that spot on the grip and if it's a 2% grade putt then that gives them the amount of break to play.
The board has lines that are ⅜ ″ apart. These represent % of grade when used in practice to determine the slope of a green. The notches at the bottom are guides for finding different widths on any club which helps give the player to determine the amount of break on any putt.