TR4A Tach Error

["Mark" <mini@nashvilletn.org>]

I am still sorting little things with my new toy.  I noticed that the tach 
seemed to be reading high (to my ear) and checked it with two modern 
electric tachs I had in the garage.  Sure enough it is about 800 +/- lower 
than actual.  Is there any info on how to calibrate a mechanical tach or 
were there different drive ratios on various TR models. I know that Nisonger 
and Mo-Ma do this type of work but the instruments really don't need 
rebuilt.

Thanks,
Mark
Nashville