Mastech cable locator MS6818

How to use! Very little out there on how to use this. One wire to ground, one to one of the wires. Signal drops off after short or cut wire. Used it in the front yard to try and locate broken underground wire, 12/2. Worked till I got out about 75&and then very difficult to locate... Transmitter Signal on 3, and receiver right on the ground, and just putting it flat on the ground, not moving, could barely get a signal, near teh end. Not sure how deep it was buried...yet.