FOLD ARC LENGTH
The shortest distance between two alternate hinge points is called the wavelength of the fold. But the actual length of the folded surface between the alternate hinge points (say, measured by a pair of dividers or a thread) is called the arc length of the fold. In case buckling is predominent, the arc length during folding remains unchanged or hardly much changed. However if the folding occurs by buckling as well as layer shortening or layer parallel strain, then the arc length gets changed appreciably, the magnitude of change is dependent upon which of the two strains is more dominant. Stubby and gentle or open folds are likely if layer parallel strain predominates. High amplitude close to tight or isoclinal folds will form if the buckling strain is more predominent. See for example the finite element results of study on buckling under different viscosity contrasts by Dieterich.