If you don't wanna buy a tach just to check it and you like tools....especially one that you will use the FUCK out of on an SN95 in the future, go to SEARS and buy a digital voltmeter. I got one for like $58. It has a setting to read RPM's by using the car's tach signal.
SO, you'll be able to set your tach back right AND in the future, you can set your TPS voltage, AND pull codes by tricking the system (any haynes manual shows you how). Not to mention everything else they're good for.
THAT would be my route....rather than buy a tach I didn't want in the first place.