There is a company out there that sells by brand name a TINY TACH. It can be found at many small engine sales and repair. It is a induction tach [digital] and so you wrap one wire around any plug wire and the other to ground. I fed mine from the ash-tray of my 444 [drilled a hole in the bottom] through the fire wall and wrapped it around #4 wire.It is so small that when I don't want it to show, I close the lid of the ash-tray GONE. It sits on the lip of the tray velcroed to the underside of the lid. While driving, it can be easily read, and when parked, it has a resettable hour meter that will let your read the number of hours on your oil;how many hours you hobby drove this or that year It is about the size of a zippo lighter [for the young ones, an I-POD] and cost 85.00 canadian. When asking to buy one; request resettable hour and for use on a true 4 stroke single fire engine . The one on my 75 H-D has seen rain, snow, and thankfully sun and that one is a 4 stroke DUAL fire. This one is three years old.
Just a way to have your tach and hide it to.
Cricket444