Using the Calculator 
The vtkArrayCalculator is used for performing mathematical operations on
arrays of scalar or vector data in a data set. To use this filter from
within ParaView, click on the button in the toolbar with a calculator icon.
Select whether to operate on point-centered data or cell-centered data
(i.e., the attribute mode). Choose a name for the array that will contain
the results of the mathematical operation. (By default, the name of the
new array is set to "resultArray".) The two buttons near the bottom of the
calculator interface labeled "scalars" and "vectors" are menu buttons that
allow you to choose which arrays to operate on. Click the appropriate
buttons and array names to set up the mathematical expression you wish to
evaluate. If you make a mistake, you can click the "Clear" button.
When you have entered the expression to evaluate, click the "Accept" button
for the evaluation to take place. The results will be stored in a new
array in the data set with the array name specified.
Last modified: Mon Dec 3 13:25:11 EST 2001