Watch expressions allow you to monitor the values of variables, properties, and expressions at run time. Many debugging problems aren't immediately traceable to a single statement, so you may need to use a watch expression to observe the behavior of a variable or expression throughout a procedure.
The development environment automatically monitors the watch expressions you define. When the application enters break mode, these watch expressions appear in the Watch window, where you can observe their values.
You can also direct watch expressions to put the application into break mode whenever the expression's value changes or equals a specified value. For example, instead of stepping through perhaps tens or hundreds of loops one statement at a time, you can use a watch expression to put the application in break mode when a loop counter reaches a specific value. Or you may want the application to enter break mode each time a flag in a procedure changes.
To add a watch expression at design time or in break mode