FOLD AMPLITUDE

Amplitude of a fold is half of the least distance between adjacent hinge points or half of the least distance between the top and bottom enveloping surfaces. In other words, it is the least distance between a median plane\surface and one of the two enveloping surfaces of a fold train. The enveloping surface can be treated as a form surface since it gives approximate orientation of the layers before folding. see enveloping surface and median surface and geometry of folded surfaces