I dropped the front panel and set the endpoints through the access hole to within 50 HZ. The linearity is not so close. It is 530 Hz off at 250 on the KHZ dial, 600 off at 500 on the KHZ dial and 60 HZ off at 750 Khz on the dial. Is it worth messing with the linearity?? or is this pretty good. It is a Dubrow PTO. Scott