The given lengths of the set-squares are, in the case of 45° set-squares the hypotenuse; in the case of 30°/60° set-squares it is the longer of the legs.
Bevelled and straight edges are usually not so great for ink drawings because the ink tends to be drawn under the set-square or ruler and when these are removed smudges can result. On a straight edge clean lines can be made with a little practice by holding the ink pen at an angle. The bevelled edge, when turned over on the other side, becomes an ink edge. (This only in the case of set-squares with no knob or ones where the knob can be removed.)