FRD and ZMA files are *very* simple. Basically a list of measurement points.
There are three columns on each line, terminated by a carriage return and line feed (unix systems often only have a line feed). The columns are frequency, measurement, and phase. The measurements are then sorted by increasing frequency.
The next problem lies with the interpretation... Should the frequency be frequency linear like in an FFT (often producing gigantic but not so useful files), logarithmic (but must have enough points to be useful), scattered? What about identical frequency entries (we strip these for ZMA and FRD export)? If points are missing, should they be filled in using interpolation, and if so by what method?
If you look at the ZMA files produced by our products, to some extent they reflect the test methodology used. When we do a TS test using a SINE signal we zero in on the points of interest, maximizing precision and reducing susceptibility to noise and non-linear effects. Therefor you will find a series of points in the table that are close to these points of interest (down to a 0.01Hz step). On the other hand, if you use an FFT bases ZP test (or the SnapTS for our ST/WTPro users) you will see a continuous progression of points, albeit interpolated to fit a log scale.
Now the question is what to do with an input. Well, all of these interpretations should be considered. If not, and if the interpretation is not too outlandish, go back and add it. In the end the product will be better off.