Quantitative measures

Performance measure.
Efficiency measurement of input and outputs is illustrated in three different situations.
1) Where input is fixed = Actual output / (divided by) maximum output obtainable for a given input
2) Where output is fixed = Minimum input needed for a given output /(divided by)actual input
3) Where both are variable = Actual output / (divided by)output input compared with standard output / (divided by) standard output
Could you kindly explain how the results of these equations illustrate the efficiency measurements? I don’t understand what is being taught here and how to apply it.