Calculates the Pressure-Intensity (P-I) Index from SPL and Intensity measurement functions. The P-I Index is defined as,
P-I Index (dB) = (SPL (dB Reference 20 m PA) - Intensity (dB Reference 1e-12 watts/m2) )
When this command is executed, a dialog box is opened.
When Calculate is pressed, a new Data Block file with P-I Index measurements in it will be created.