In DM2000 Calculator window has several functions. First, unlike standard Windows calculator, this tool allows you to evaluate arbitrary expression that may depend on the set of variable parameters (see expression syntax for more information about available functions and operators). You may change values of a..z parameters using Parameters table and calculate result for several parameter sets. The result of calculation may be automatically copied to the clipboard.
Another application of the Calculator window related to the Plot and Worksheet calculator tools. These tools use expression defined in the Calculator window that can be evaluated for selected curve point or worksheet line. Both tools work exactly as you would click "Evaluate" button in the Calculator window, but the Parameters table specially filled before calculation.
Note that both Plot and Worksheet calculator tools display evaluation result in status line of the main window.