I bought a car once from a garage who's top mechanic was totaly deaf. You could
bring a car in, he would go around touching the engine in different places, and lean
against the fenders in different spots. He would walk away, come back with the
right tools, and after a minute or so, the thing would start purring like a kitten.
A tach isn't always necessary, but I still dont see why they dont come standard.