Bill, I can't give you much advice on purchasing the replacement ASI. Some people get an overhauled one.
I bought a low-cost new one with TSO paperwork (which I later suspected since the source mail order company was later charged with selling counterfit stuff). Still, my replacement ASI worked perfectly. As for calibration, look near the bottom of this article on my Coupe website: http://edburkhead.com/Ercoupe/airspeed_indicator_errors.htm Ed Ed Burkhead http://edburkhead.com/Ercoupe/index.htm East Peoria, Illinois ed -at- edbur???khead.??com (remove the ? marks and change -at- to @)
