Look on the back of the tach on the 3 inch diameter protruding part. In the area behind the 40 on the face is a hole. It may be covered with a rubber plug or a sticker. Behind that hole is a calibration adjustment that can be made with a small screwdriver. Keep the tach upright in its proper position when making the adjustment. See if that helps.
Look on the back of the tach on the 3 inch diameter protruding part. In the area behind the 40 on the face is a hole. It may be covered with a rubber plug or a sticker. Behind that hole is a calibration adjustment that can be made with a small screwdriver. Keep the tach upright in its proper position when making the adjustment. See if that helps.