J.S.W Calculator--K35

I have an old whiz wheel that is apparently used to calculate height
needed to cover a specified distance. I got it with my Libelle 201B.
Was just looking at it and trying to figure it out. It has a
semicircular rotating part on the front with Height Needed across the
top and a speed scale across the bottom (flat side). On the fixed
card, the outer scale is Nautical Miles to Go and there is a wind
component graph at the bottom left and upper right. It looks like I
put my speed to fly over the wind component and then read altitude
required under the desired distance. Does anyone know if that is
correct? Also, I think it's missing a piece on the back. The back of
the whiz wheel is labeled JSW Wind Component Resolver. The brass hub
is there, but there's not any moving part, which I suspect is
required. It says made in England, Copyright 1986 JS Williamson. Can
anyone give me more information about this little device?