PURPOSE: To provide an absolute deformation degree estimating method by which the same evaluation can be obtained if a deformed shape is the same and a deformed condition can be easily grasped in essence.

CONSTITUTION: From coordinates of a point A, a point B, and a point C, a formula for a regression plane is found by a least square method, and then, minimum distances δA, -δB, δC from the respective points A, B, C to the regression plane are found. If δC is assumed to be larger than δA, a closer resemblance to a plane is accomplished when a total of an absolute value for the maximum value on the (-) side and the maximum value on the (+) side is smaller, and it is evaluated that the degree of deformation is small.