Eliminating Errors with Error Tracing in Formulas
Despite your best efforts, it's almost impossible to prevent all formula errors from cropping up. Possibly the worst thing about this is that the errors often tend to spread far and wide, given the web of formula interdependencies in a spreadsheet. The biggest challenge in such situations is to track down the root of the problem - that is, the cell with the original formula error that causes the error values to sprout up all over the place like dandelions over a field after a spring rain.
Fortunately, Excel offers some effective tools for tracking down the cell that's causing your error woes by tracing the relationships among the formulas in the cells of your worksheet. By tracing the relationships, you can test formulas to see which cells, called direct precedents in spreadsheet jargon, directly feed the formulas and which cells, called dependents (nondeductible, of course), depend upon the formulas' results. Excel even offers a way to visually backtrack the potential sources of an error value in the formula of a particular cell.