I had the tech run it on the bench with his digital cable driver from 1000
up to about 3500 RPM and the tach readout matched at each stage. I also
checked with my optical tach through the windscreen at 2500 and got a match.

Before the overhaul 2500 on the analog tach gave me 2580 on the optical
tach. I started to investigate the tach when I couldn't understand why the
static RPM on an obviously strong engine didn't meet the minimum book value.

I also learned from this exersize that the error was not proportional i.e.
an 80 RPM error did not translate to a 40 RPM error at half the speed.

--
Regards,
Mike

http://mywebpage.netscape.com/amountainaero/fspic1.html
"Jon Woellhaf" wrote in message
news:riRcd.414274$Fg5.254744@attbi_s53...
Mike Noel wrote that he had his analog tach overhauled and that it is,
"...
now giving accurate readings across the RPM range."

Mike,

How do you know it's accurate?

Just curious.

Jon