The difference and total value of the spectrogram can be calculated and output using ”ExpressionItem” of FFT.

1. On the FFT analysis screen, set the two data to be calculated as “before countermeasure” and “after counter measure”.
2. Double-click ”ExpressionItem”, “Inter-item calculation” will be displayed.

3. Double-click “Item”, “Operator/Function” in the list, input SQRT([1]*[1]-[2]*[2]), then click “OK”.

4. After the operation executed, the differences value between before and after countermeasure will be displayed in brown line.