The Watch Window feature in Excel 2010 lets you keep tab on any selected window. This comes useful in situations when you need to verify particular data/formula/function against some other data set or verify changes in formula/function with varying data. Lets take a look at how to use this feature.
To start out, select the data range which you want to consistently observe for any change. Now head over to Formulas tab, and click Watch Window.
This will open Watch Window, click Add Watch to start watching selected range. Click Add to add the data range in Watch Window.
When clicked, it will add the watch for values and formulas of specified range so that you can always keep the data range under yours observation.