Probably more than 200 Dwayne. If you've got the 485 engine, I'm thinkin' you should be able to rev to at least 2400. The tach sending unit is screwed into the side of the bellhousing so it can count flywheel teeth. With the tractor NOT running, loosen the locking nut and carefully screw the sending unit in till you feel it touch the flywheel. Back it out a quarter turn, and tighten the lock nut. See if that doesn't accurize your tach readings some. It may take some fine tuning, cuz closer is better. But finding the sweet spot can cost you a sending unit if it gets hit by moving flywheel teeth. Careful.
//greg//