The tachs in our B110 are triggered via an inductive loop, there is no direct electrical connection. The pointer is able to sweep through ~ 270 degrees. after that it just maxes out at the and will not move any futher due to physical limits.

The cct is able to be recalibrated to different scales but it is worth noting that these type of tachs inherintly have a percentage error. I get my tachs calibrated and certified by a qualified instrument repairer, [just because i am a fuss pot]. This also includes re-balancing the needle and adjusting the counter balance weight and tension spring . Due to this precentage error it is far better to be spot on [indicating] at say 8,000 RPM where it matters rather than at idle speeds.

In recent times I have been sucessful in making reproduction 10,000 RPM competition tachs.