Degrees Without A Compass
: THE USES OF THE COMPASS AND THE SQUARE
But in the absence of a compass and when you do not wish to step off a circle, you will in such case lay down the square, and mark off at the outer margin of the limbs two equal dimensions. Suppose we take 2 inches on each limb of the square. The angle thus formed by the angle square blade is 45 degrees. To find 30 degrees allow the blade of the angle square to run from 2 inches on one limb to 3½ inches on the other limb, and it will be found that for 15 degrees the blade runs from 2 inches on one limb to 7½ inches on the other limb. It would be well to fix firmly these three points, at least, in your mind, as they will be of the utmost value to you. It is a comparatively easy matter now to find 10 degrees or 25 degrees, or any intermediate line.