Ex. 1a-f below show the established indications for flexion and extension. The indications for flexion can be interpreted as contracting, folding, or joining. However, they only contain the signs for contracting and folding (and an ad lib. sign). Likewise, the indications for extension can be interpreted as elongating, unfolding, and separating, but they only contain the signs for elongating and unfolding (and an ad lib. sign).

I think the signs would be clearer if they included all variables. For example, the signs for flexion could contain the signs for contracting, folding, and joining, as in Ex. 2a-c. The signs for extension could contain the signs for elongating, unfolding, and separating, as in Ex. 1d-f.