How do you find out a sail's size when it is not marked on the sail? Can it be measured?
I have an Arrows Flight Freestyle sail, I think around 2004 age. Gold and silver in colour. Searched the web and only found 2005 onwards and some of this refers to a gold/silver sail of 2004 vintage, but no stats or photo's.
Cheers
Lay it over sails you know the size of? This would give an estimate at least unless the sails are completely different in shape.
Rig it and go for a sail. Then if...
Underpowered => size = too small
Overpowered => size = too big
Comfortably powered => size = just right
(for more details please consult the Goldilocks manual) 
There is a way to measure but it is overly complicated, one of the old raceboard boffins will be able to tell you.
Take a closer inspection around the foot, on proto sails it is often written in pen under tack or on the foot panel.
If that fails easiest way other than overlaying is rig to find out mast & boom measurements, then compare to other similar sails of that period.
Luff Length (m) X Boom length (m) X 0.75 will get you as close as you will ever need.
4.64 (mast) *1.94 (Boom) *0.75=6.7m^2
The reason its 0.75 instead of 0.5 is to take into account the roaches. The roach factor could be anywhere from 0.7 to 0.8 but it shdol eb close enough.
JB
That's pretty close, but in my cases it gives 0,3m^2 more than actual size. But still good.
Check out maui ultra fins site. I remember seeing it showing you how to calcutate fin area. Should be the same for a sail I thinkhttp://www.mauiultrafins.com/MUF7_english/FAQ.html
Just pin it out flat and break it up into 4 triangles. The one which will encompass the luff curve you can multiply by something like .66 to allow for the curve. It is primary school maths, no calculus or differentiation needed. But it would be much easier to lay it over similiar sails and make an educated guess.
Interesting to know
The RSX is class legal as a race board. Race board sails are 9.5m max. If you lay the RSX sail over a 9.5m sail it is bigger.
I have read the RSX 9.5 is actually 9.8m
