The Heathkit SB-650 Frequency Display is designed to operate with Heath amateur receivers and 5 band transceivers of the SB and HW series operating in the 3 to 30 Mhz range. It calculates the received frequency to 1/10khz and displays the frequency on six display tubes. The only operating control is a front panel rocker switch which turns the instrument on and off. These are rare items only produced from 1972 to 1975. I have no way to test this unit but it worked when it was last connected to a SB-303 receiver. I am including the original Heathkit manual to go with it for $295.00 plus shipping costs. No International or shipping outside the Continental US. USPS Money Order or cash only.