[EICO] Date from Serial No.?

[Daddio683@aol.com]

I have a 955 Capacitor Tester and I just got another one for repair.
One has a brushed aluminum front panel with dark gray screened printing and 
the other has a painted front panel (light gray) with white print.

Does anyone know the formulation of the serial numbers so that I can tell the 
date when each was made?

My manual has a copyright date of 1962 but does anyone know when they started 
to make these and for how many years?

Regards,
 Gary.