Plumber's Rule

A131 $19.75  

Dimension-5/8" x 6 foot
Two sides: Regular scale/45°scale

How to Use: To determine the length of the long side (Hypotenuse) of a 45° right triangle, place your thumb nail on the length of the leg on the regular scale and turn the ruler over. The length on the 45° scale side is the length of the longest side (hypotenuse). To find the length of the leg, place your thumb nail at the correct measurement on the 45° scale side and turn the ruler over and read the regular scale.
For example, look at the rules on the left. Notice that 3" on the regular scale aligns with 4 1/4" on the 45° scale.