Knowledge of leakage inductance is also useful when transformers are operated in parallel. It can be shown that if the percent impedance[e] and associated winding leakage reactance-to-resistance (X/R) ratio of two transformers werethe same, the transformers would share the load power in proportion to their respective ratings. However, the impedance tolerances of commercial transformers are significant. Also, the impedance and X/R ratio of different capacity transformers tends to vary.[15]