A Watch expression is essentially what its name implies; it is an expression
whose value you want to watch change while your program runs. The expression may
be simple or complex.
A simple expression might consist of a single variable. A complex expression
might perform calculations on multiple variables, or even call functions. The
only requirement is that a Watch expression must be a legal VB expression. In
other words, if you can’t use an expression in a line of code without generating
a compiler error, you can’t use it as a Watch expression either.
Creating a Watch Expression
Types of Watch Expression