Johnson Level & Tool Mfg. RAS-1 - Manual (Page 29)

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roof. For a pitched roof, use the angle scale and make your
mark next to the angle that is the result of the roof inch rise
angle minus the overhang inch rise angle.
DEGREE SCALE
With the degree scale on our square, any angle can be found
on a board. Figure 16 shows a couple of examples. To find an
obtuse angle, for example 105°, put the pivot point on the
mark where the cut is to be made. Lay the square so that the
“T” bar is held tight against the board and draw a perpendicu-
lar line across the board. Now flop the square on its opposite
side (making sure you’re using the same pivot point) and pivot
the square so the degree scale reads 15° (105° - 90°). Scribing
a line along the bottom edge of the square now gives you a
105° angle (and also a 75° angle and a 15° angle).
FIG. 16 Resulting Angles Using the Degree Scale on a Board.