The apparatus (1) has a monitoring and control unit (10) arranged to read, at successive regular time intervals, an indication of relative angular position of a handle (11), and to act on the adjustment setting based on indications of current relative angular position and of preceding relative angular position that are read respectively for current and preceding time intervals. The monitoring and control unit is arranged to compute a current angular difference based on indications of the current and preceding angular positions and to compare the difference with a preset threshold.
