What does the "P" mean on my 230 Micro Pump adjustment know

The “P” stands for priming position preferred. All 230 Micro Pumps are self-priming and can draw a vacuum, but the adjustment knob must be all the way down and the “P” lined up with the mark on the pump body, indicating it is in the priming position. It is preferred to leave the pump in the priming position during normal operation unless the desired output cannot be achieved by reducing the cycle rate. This will ensure any air bubbles will get pushed through the system if the reservoir runs out of fluid.