Speedo and rpm problem

[HulettChance]

First my car is a 1990 s13 with a rb25s2 in it with the trans also. When I got the car back in September the guy that owned it said nothing on the cluster works except the fuel gauge... So I dug into it and it was simple fuses that were blown I replaced them now the cluster works but me speedo reads half what I'm doing, I'm going 60 it reads 30 also my Rpms are about half of what they are I have other gauges for rpm boost water temp oil pressure I didn't know if it had to do with something simple as a sensor as such? Any input please

[PapaSmurf2k3]

I think you need a different tach for the 6 cylinder, but there is a calibration adjustment for the speedo. I'm not sure if it has enough adjustment to double your speed though :/
Basically you remove the cluster and then there's a little plastic screw type thing on the speedo circuit board.