The sonic tracer helps you to grade, level and backfill better on irregularly-sloping ground. It emits a sonic signal to maintain a set distance or elevation from a particular object, surface or the ground. Installed on the blade of the grader, the sonic tracer enables it to be used to grade, level and backfill on a multi-slope terrain, when following a string line, kerb stone or gutter, or even on a previous pass for a grade control.