Switching a pump from Auto to Hand changes who controls it, so the switch raises the positionRequest event and shows the requested position as pending until the application reports the value the plant accepted. With the confirm property enabled, the position has to be pressed twice. A complete control station with a selector, start, stop and jog buttons is shown on the Momentary Button page.
Press a position. The switch shows it as pending, the simulated plant answers after a moment, and the switch takes the position the plant reports. P-2101B has confirm set, so its rotary selector arms on the first press and requests on the second. The duty selector has three positions with descriptions, which are read by screen readers and shown as tooltips.
Keyboard: each switch is a radio group. Tab to it, use the arrow keys to move between positions and Enter or Space to request one. A pending position and a refusal are announced to screen readers.
The switch a panel would carry, drawn above the same row of positions: a toggle lever that leans to its position, a rocker whose pressed face is lit, and a slide whose knob sits at its position. The row of positions stays the control that is pressed and read; the drawing follows the position the plant reports, and shows a pending request in the pending colour. These are the toggle switch, rocker and slide switch of a test-and-measurement front panel with the request model of the line.
Press a position; the plant confirms after a moment.
An interlocked switch stays readable, shows the reason and raises the blocked event when pressed instead of a request. A request that the plant never answers is dropped after pendingTimeout, and the switch returns to the position it had.
The recirculation selector is wired to nothing: request a position and watch it drop back after 2.5 s.