Pump Curve

Does anyone know if a pump always operates on the performance curve? We did a test on a pump. We monitored the flow and the head it delivered, and found out the data was off the pump performance curve. The head may not be accurate. If the pump always operates on the curve, we can use the curve and the flow to find out the real head it delivered. Can anyone tell me if this is a right way to do? Thanks!

With a new pump, I have always been able to rely on the pump curve. They are usually close enough that if I know the flow and pressure, I can determine the water level in the well within a few feet.

My pump is not new. Is the pump curve still reliable?

Only if the pump still works like a new one. If it is worn at all, the performance will not follow the curve.