My gaffrig tach is 250 rpm low,next to a shop tach while on the water running.is there any way to adjust this?

Is it possible Gaffrig gauges aren't consistant? I'm having similar problem with water temp and oil pressure gauges.

I have seen a lot aof problems with all of thier guages accuracy along with just about everyother brand out there. What we gound to work best was to keep about 20 of each sender in stock and find one that read high and then install a resistor to correct them. 10 ohms is about 5 degrees on water temp and about 3 psi on oil temp. This will not work for the tach though becuase they are a rev counter that count pulses, instead of a thermistor or potentiometer. Some of the gaffrig Tachs have an adjustment screw on the back though next to the cylinder selector switch.

first make sure you have it set on the correct cyl setting on the back of the tach. Theres also a way of setting the tach up yourself if you happen to have a signal gennerator. Or just send it back to them and let them know its off....i'm sure they would stand behind their product and fix it.

Mine is within 50rpm.

My tachometer is low by a couple hundred RPM's at 4000 (about 5%). I keep thinking that I should remove it and have them recalibrate it, but haven't gotten around to it. If you are calculating slip and your tach is off by 5%, your slip figures won't be accurate.