Now lay out the angle on paper, thus:
The line above and parallel to the circumference line must be placed in a position making the distance between the two lines equal to the specified pitch, which is, or should be, marked upon the boss of the propeller.
Now find the circumference of the propeller where the pitch angle is being tested. For example, if that place is 2 feet radius from the centre, then the circumference will be 2 feet x 2 = 4 feet diameter, which, if multiplied by 3.1416 = 15.56 feet circumference.
Now mark off the circumference distance, which is represented above by A–B, and reduce it in scale for convenience.
The distance a vertical line makes between B and the chord line is the pitch at the point where the angle is being tested, and it should coincide with the specified pitch.
You will note, from the above illustration, that the actual pitch line should meet the junction of the chord line and top line.
The propeller should be tested at several points, about a foot apart, on each blade; and the diagram, provided the propeller is not faulty, will then look like this: