An adjusting device for a sensor unit mounted on a field machine, or a harvester or tractor, and an associated method for positioning the field machine and sensor unit for locating a working edge of a field. The sensor unit can be mounted on a cutter bar assembly of a field machine via a supporting arm. The sensor unit may be adjusted horizontally or vertically. The sensor produces a signal that is communicated to a steering control unit to guide the field machine along the working edge of the field. The position or alignment of the sensor unit relative to a working edge of the field may be indicated on a two-dimensional display.
