What does it mean by 'watch' in context of the debugger?

Instead of pointing mouse pointer over a variable to show its value or using the Locals to view the values of all the local variables, you can also add only interested variables in the Debugger’s Watch Window (accessible through Debug -> Windows -> Watches -> Watch 1). The values in Watch window are always visible in the bottom of your VS.Net. To add any variable to Watch Window, right click on the variable and choose 'Add Watch' or drag it to the watch window.

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