This dialog is activated by selecting the **Subtract -> Reference Data** command or the **Math on Data Sets...** command from the Analysis menu. With its help it is possible to perform basic mathematical operations (additions, substractions, divisions and multiplications) on data curves.

By pressing the *Apply* button, the arithmetic operation selected in the
*Operator* list box is applied to the current data *Curve* and to a second
operand that can be either an existing data set (a *Table* column) or a custom
*Value* entered by the user. The last operation can be reverted by pressing the
*Undo* button.

If the second operand is a table column QtiPlot might also use a linear interpolation on the values of this column and the abscissas of the data curve to be modified before performing the requested arithmetic operation.

By checking the *Current folder* option, only the tables in the active folder of the project are displayed in the *Data set* list box.