Allis Chalmers Tach - backwards?

[dhermesc]

I found an Allis Chalmers Tach (marked as such and Made in the USA). It looks just like what a 180, 185, 190 would have and reads from 0 to 2500 RPM (also has hours) just like a one of those. Except this one the needle sweeps backwards - turns counter clockwise as RPM increase. Every other tach I've seen (car, truck, tractor) the needle sweeps clockwise as the RPM increases.

Any idea?

 

[Dieseltech]

Some MF tach's turn counter clockwise.

 

[Dieseltech]

Might be for the three cylinder Perkins diesel used in the AC 160, the MF 135 with the same engine tach turns backward.

 

[DrAllis]

Does it say ALLIS-CHALMERS ??????? I'll bet it says AC....which stands for AC DELCO, not Allis-Chalmers.

 

[gatz271]

D17 gas tach was CW, Diesel was CCW