Hi natandmark,
That is exactly what we do.
There is an explanation on how we calculate IMD on page 185 of our User Guide here:
https://www.picotech.com/download/manua ... -guide.pdf. For the measurement we look for the 2 highest peaks as F1 and F2 (you can specify over what width a peak will be detected) and calculate IMD using the second order components.
Although the User Guide example shows a decibel calculation (which would be dBc) we provide the value as a percentage (which is just replacing '20logbase10' by 'x 100').
Regards,
Gerry