I was recently cleaning some old tachometers and needed a way to check them. I used a 250 inline 6 distributor and a battery. I chucked the distributor shaft in my drill press with the cap facing down. Using the slowest speed and a rubber stopper (to keep housing from turning) I was able to check the meters at a set rpm. I had four meters hooked up at once so it was easy to see which ones didn't read right!

Four a quick test, it worked really good with no problems.

Joe