This calculation is trial-and-error since yr,N must be guessed. A loop using Eq. (17-78) to converge on the correct value for yr,N is used with an arbitrary number of trials M (in this example M = 5). The spreadsheet inputs the required values. All calculations of the equations in Section 17.7.4 are done in the Visual Basic program. The spreadsheet is shown with values for the separation of oxygen and nitrogen in Example 17-11. Note that a very poor first guess for yr,N = 0.001 (not shown here) converged with M = 10 to the correct yin.