Device with an operating parameter whose value can be preselected by means of a control unit

An apparatus having an operating parameter associated therewith, said apparatus being operable in a plurality of successive activation phases having respective time durations with said activation phases being respectively separated by time intervals, said apparatus comprising

• a control unit which allows entry of different duration for providing a selectable value for said operating parameter which will be effective in at least one of said activation phases;
• a display connected to said control unit on which said activation phases are shown along a time axis as respective rectangles, each of said rectangles having a length along said time axis corresponding to the time duration of the activation phase represented by that rectangle, and each of the rectangles having edges respectively indicating a beginning and an end of the time duration of the activation phase represented by that rectangle, with respective spacing between respective edges of successive rectangles representing said time intervals, and a height of said rectangle a right angle to said time axis within the rectangle representing the value of the at least one activation phase in which said value of said operating parameter will be effective;
• and
• an actuatable enabling arrangement connected to said control unit which must be actuated in order to allow said value of said operating parameter entered via said control unit to take effect in said at least one of said activation phases.