Cheap Tach?

[Midnite]

After turning up the pump on my '92 a little bit, I also needed to turn down my idle speed. Unfortunately with no tach about all I can do is turn it down to a speed that SOUNDS right and still gives me a reasonable oil pressure reading on the dash gauge. However, I'd rather trust a tach instead of my ears.



Does anyone know of a quick and dirty tach, like maybe some way of hooking a multimeter to the alternator, or something similar?



Thanks,

Mike