SurferKris said..
On my RAF sails (from other brands) I usually look at how far "forward" the top panel gets loose. One can even put two small pieces of silver tape there in order to indicate the max and min settings (placed after a successful session in each wind range).

Thanks
I have a visual cue, too, on my sail, It is a narrow, horizontal label on the panel with captions "Min" and " Max " towards the leach and towards the mast, respectively, but it is not easy to spot where the sail starts being loose in relation to these markers, because the sail material is transparent.
This is why I prefer to take the leach line as a cue and see how far it extends down towards the boom.

Francone