To me, double weighting, like others have stated, is about losing changeability. At the point of contact, this would be like touching a side of a cube (flat = double weighted) in contrast to a sphere (round = changeable). Now a cube can have a quality of changeability if the point of contact was at an edge or a corner, and a sphere can lose its changeability if it deflates/collapses and the point of contact penetrates inside the outer circumference of the sphere (no longer having the point of contact the farthest point). Changeability is about being able to have Yin+Yang at the point of contact rather than having Yin+Yin (deficiencies, collapsing...) or Yang+Yang (excesses, resisting...).
In the feet this is a little less easy to explain since all of the joints between the point of contact and the feet contribute to the changeability. But basically, things like bracing (resisting...) will be a noticeably fixed and unchangeable response that I would point to as being double weighted (regardless of weight distribution between the two feet).
This. Excellent description and the same as my understanding of the term. I am currently writing an article on some of the points above, so it is nice to see it so well summarised.
IMO the idea is called 'Double weighting' because when you are not changeable (cannot use Pairing in my description of the process) you inevitably become responsible for the opponent’s 'weight' (or force) as well as your own. Hence, doubling the weight you are responsible for.
In the solo practice we can inadvertently train ourselves to limit our ability to ‘change’ when interacting with another person. Usually this is manifested in un conscious tension, moving outside of the optimum range for the joints to easily rotate or change angle, collapsing the structure (most notably seen in the knee or elbow), Locking joint angles (moving like a robot), etc etc. So it is something that can, ultimately be applied to the legs or feet, but as said above doesn’t really represent where the weight is distributed between them.
thanks.