This unit seems to be quite superfluous when used with a USALS motor and a modern receiver. The receiver can generate move East and West and GoTo zero commands and will also calculate the GoTo X commands which will point the rotor to the correct azimuth angle to receive a particular satellite (assuming the the rotor and dish are aligned properly to begin with). Have you input your location correctly into the motor/rotor settings in the VU receiver menu? With the correct location in the receiver, the receiver just sends a Disecq GOTO X command to the HH120 motor and it should turn east or west to point at the correct satellite. The receiver does not know where the motor is pointing to currently - it just tells the motor to turn to absolute angle X either east or west, depending on the satellite you've selected to tune.
Here's a screenshot of my USALS config for my dish:USALS_setup.jpg
Here's a screenshot showing manual move and goto facilities:USALS_move.jpg