The Turbine is tested under a constant head H for each of several gate openings, and the values of Power output P and speed N are reduced to unit conditions ( Equations (125) (132)). Suitable values for efficiency are then marked on the curve for the differing Gate openings and lines of iso-efficiency are drawn
These graphs enable the best running speed or the best gate opening to be chosen,as well as the corresponding power output for that speed and gate setting to be found for any particular head.