Please allow me to suggest a new concept: "real airspeed" or "RAS"  RAS is
defined as TAS reported by the airplane or kit manufacturer times 80%.  There
is also a formula for detemining RAS based on TAS as reported by the owner.
  Unfortunately you have to apply one of the following three concepts to the
owner:  "truth teller", "fibber" or "bald-faced liar".  The discounts from TAS
are, respectively, 5%, 10% and 30%.  A friend constantly wonders what it is
about him that causes experimental a/c to slow down by 30 kts. whenever he
gets in them.  The concept of RAS should take care of the problem.  Fly safe
-- you'll live to brag.