USAAF Synchronism indicator

Hi all, another quick question.

I have a Strobomeca visual tachometer made by the Boulin Instrument Corp of New York. Its servicable and boxed. Comes with a USAAF data plate listing it as a type C-1 Synchronism indicator. Its serial number is 45 and its Strobomeca number 28.

The AAF packing label lists it as a class 06B instrument. Its complete with discs for 2 blade and multiblade propellers.

Couple of things:

Any one got a hand book for it?
Does it have any rareity value?

Photos to follow when I’ve found what i’ve done with my camera!

Rgds

FB