What I would like is for you to try your code on your spreadsheet.

Yep - a simple, but nonetheless valid unit test. Calculate the expected output in your spreadsheet (you might even include rounding/truncation if you're using integer or fixed point arithmetics in your program), and then check the output of your code against the output of your spreadsheet. If they differ, you've got a bug (either in your spreadsheet, or in your code).