Health index / performance curve of a motor
The paper that you cited seems to provide the necessary information. The paper shows that the numerical results of various tests are normalized to 0-10 index values and weighted as described. The index values are then combined and plotted. You will need to search for the individual tests to find how the values are determined from the tests. You should read each of the papers cited in the paper. You should also search for subsequent papers that cit the paper that you cited. That may provide some additional clarification and indicate whether or not this "health index" has been well received.