I had not played with the arc calculator for a long while .

http://myweb.tiscali.co.uk/mx5alan/arcs/wind_range.htm

I have found it fun and interesting.

One very interesting thing is that they rate the 15, 19 and 24m Synergy as having the same bottom end as each other in my weight class . About 3-4mph. Each naturally has a different and realistic top end.

I love my 15m Syn' and can work a ride out of it in amazing low winds but there is still plenty of room under it for my 18m Phantom (and 19 Speed). The calculator says I should get equal bottom end out of my 18m Phantom but I find a notable difference in bottom end between the 2 ?

Is my 15m Syn' a bit of a dud' . It was one that benefited from extensions on the back lines. Do the 15m Syn' and 18m Phanny have equal bottom end in others experience ?

No. I've owned both and the 18 phanny rules in this battle. It's odd the calculator makes that mistake.