In a swather formed by a tractor and attached header for cutting standing crop to form a swath, reel speed and optionally draper speed are controlled relative to ground speed by a control system including a manually operable input and display available to the operator. The control system acts to calibrate" the control output so that the control module has a secondary reference point as to how the PWM valve should function in the event of a speed sensor failure. Instead of using the speed sensor signal as a reference, the control system now compares the set point with the stored table (which may in one example provide 256 values) containing the PWM voltage/current values. These values correspond to a set of actual speed sensor values taken during the profiling procedure, plus extrapolated values equalling 256 points.