Below is given a method of testing a carpenter's square. Shoot the edge of a piece of board quite straight, apply the square as shown at A (Fig. 1), and draw a line; then turn the square as at B, and if it is true the blade should lit the line; if it is less than a right angle it will be as shown at CD (Fig. 2), and if more than a right angle the defect will be as indicated atEF (Fig. 2). If the blade has moved or has been knocked out of truth through a fall, it should be knocked back into its proper position and, when true, the rivets should be tightened by careful hammering. If the blade is quite fast in the stock, but untrue, it must be filed true to the stock.

Fig. I.

Fig. 2. Testing a Try-square.