L-R is the side adjacent the angle.
R (radius) = the side opposite the angle.
R = just the radius.
“B” = ½ the whole angle.
Here’s what’s going on:
This is a simple right angle trig problem using the tangent function:
“L” is what we need to know in order to set the blade length on the combination square.
Part of “L” (L-R) is right next to our half angle; it is adjacent the angle.
“R” is clear on the other side of the triangle; it is opposite the angle.
The side adjacent the angle equals:
The side opposite the angle ÷ the tangent of the angle.
Once you find the side adjacent, you just add the radius to it for the blade length.