Bench test factory Mopar tachometer

The thing about a distributor is that unless you have some way of measuring it's speed, you don't know if the tach under test is accurate

I once checked my Autometer by downloading a few audio tone files off the internet. These are easy to find in the music world. I took an old "wall wort" and the easy way is if you find one that is AC output. This means it's a low voltage output direct from a transformer, with 120V at the other end. You connect the low V side to your sound card output and connect the HV side to the tach trigger. There was a thread long ago about this.

Then you multiply the tone frequency to find out the equivalent (whatever) 4, 6, 8 cylinder trigger freq.