I really meant specifying two end points and a value for the lowest point of the chain. It becomes a problem in solving for a parabola using 3 known points.

actually building a chain is not too complex because you can build it in a straight line along an axis, so only a distance from the start needs to be calculated.

I should have put up a picture to illustrate the chain joint issue. I know a few people have tried extra bones between links but I could never get that to work.