EXCEL FLAGS MOST ERRORS with a message such as #NULL! Or #NA, and if you like, it can even add a small triangle to the upper corner of an error cell. You can then go hunting through a worksheet looking for these messages and little flags (if shown) and correct formula errors one by one.
Another way in which you can check a work-sheet for errors (whether or not you display error flags) is to have Excel point the errors out to you, one at a time, like a spelling checker. Follow these steps:
Click the Error Checking button on the Formulas tab. The Error Checking dialog box highlights the first cell with an error, as shown in Figure 4-5.
Figure 4-5. Cells referenced in a formula are surrounded ...