This is a bit off the subject, but a friend much better at trigonometry than I am said to calibrate True Airspeed: Fly at a fixed indicated airspeed ( say 150 mph indicated) at 360 for a minute, record the ground speed and true airspeed; then do the same thing for heading 120, then again for heading 240 . Add both, divide by 3, and see if they match. If your Ture is a bit low, consider ( after determining no static leaks) putting a dam in front of both static posts to bring IAS up into actual.
Regards,
Gary