Proportion Between Ra and Profile on Steel (Sandblasting)

By profile do you mean peak to peak?

Rz is the average peak to peak.

Check whether this article or this helps.

Please note that these all are basically statistical (and that has to be obviously) after all you are doiing all your measurements over a small sample of the total surface (linear traverse of the pick-up and that too over a few millimeters cut-off length).