Why need of circle diagram in induction motor?

Circle diagram of an induction motor is plotted set of lines , arcs, and angles graphically depicting induction motor performance, derived from simple no-load and locked-rotor tests. A motor's "conventional" efficiency was determined based on four losses only: stator and rotor I2R, core loss, and friction and windage. Each of them could be evaluated with acceptable accuracy from tests without shaft load, through use of a circle diagram. Other than this all operational performances of an induction motor can be calculated by circe diagram without actually loading the machine.You can not count the advantages of the circle diagram only when you use it.