Steve,
I believe the question has already been answered, so my input would only be repetitive. The only thing I will add is that I believe the very first fully electronic SST tachs used a white needle with the blue line rather than the customary red one (as shown on one of Joe's tachs). I have one dated '64 that way.
This one was purchased in '69. And much to SUN's credit, it's still functioning perfectly.
Verne