I would add to syjos' post that even though I had the sending units on my engines, my tachs had the adjustment screw on the back. With that said, I noted that moving the adjustment screw with another watching the dial resulted in a limited range of needle movement which was not always linear, but it did improve things somewhat. With four tachs in the boat, I remember wishing that digital tach conversion was not so expensive. With one tach now and a need for more accurate tach reading on a planing boat, I quickly changed to digital after I bought this vessel.