The m.s.e. was calculated over non-zero pixels in each p-image within a subject's total sample according to m.s.e.=1N∑(I0k−Ikk)2, where N is the total number of non-zero pixels in the mean image, I0 is the mean of the subject's overall sample and Ik is an individual pedobarographic record. The CV was calculated over non-zero pixels in each pedobarographic image within a subject's total sample according to CV=ms.d.×100, where m is the mean value of each non-zero pixel over all pressure images in the sample, and s.d. is the standard deviation of the sample across all p-images in each subject's dataset. Each value is multiplied by 100 to produce a percentage classed as high (more than 5%) or low (less than 5%) . Very low levels of variability are considered less than 3% .