A difference in airspeed begs the question, which one is right (or less wrong)?
End the pain and find out. A few minutes of work will produce an amazingly accurate Manometer to verify airspeed indication - and by extension airspeed indication calibration.
PM me your email address and I’ll send the PDF file that converts water column height to knots. Just make sure you print it out full scale.
Note - spent yesterday helping a neighbor with pitot/static leaks on his Archer. This Manometer is a perfect tool for the job.
Note#2 - no need to remove the instrument from the plane. Just connect to the pitot tube using appropriate size tubing and electrical tape.
Carl