Payback Period (Pt, 静态投资回收期)

The time it takes to pay back the investment, i.e., the number of years required for CIs to be just equal to COs.

   t — Year at the end of which the cumulative NCs is positive.

Decision Rule 

If Pt ≤ N, the project is economically justified.

If Pt > N, the project is not accepted.

Simple Rate of Return(简单收益率/投资效果系数)

Simple Rate of Return is the inverse of Payback Period 

If a project is perpetual or its service life is extremely long with infinite uniform cash flows,

Simple Rate of Return can be used to roughly represent the IRR of a project. 

Discounted Payback Period (Pd, 动态投资回收期)

The time value of money is considered.

Decision Rule 

If Pd ≤ N, the project is economically justified.

If Pd > N, the project is not accepted.