irr refers to InternalRateofReturn(IRR).

internal rate of return is the discount rate that the total present value of capital inflow is equal to the total present value of capital flow, and the net present value is zero.

if computers are not used, the internal rate of return should be tried by several discount rates until the discount rate with a net present value of zero or close to zero is found.

internal rate of return is the rate of return that an investment is eager to achieve, and it is the discount rate that can make the net present value of an investment project zero.