How do I find formula errors?

Something is wrong with the spreadsheet. How do I find the error?

If you can find values on the spreadsheet that are either wrong or right, Xing out wrong values and checking off right values will help you to find errors in the formulas.

What do the yellow and orange cells’ interior colors mean?

The shades of yellow and orange highlight which cells might have a formula error. At least one of those cells definitely has an error -- the darker the color, the more likely that cell is the one with the formula error. You can narrow down your search for the cell with the erroneous formula by making more decisions about cells’ values (with checks and Xs). This will make some cells even darker and others even lighter.