Boxplots of the change in inter-marker distance. For CT1-CT2, CT2-CT3 and CT1-CT3 the differences in absolute vector length are shown, as well as for the three separate directions (L-R, C-C and D-V). The dashed horizontal line represents the line of no change in distance between marker pairs. The boxes itself represent the first and third quartile (lower and upper edge), where the horizontal line inside the box represents the second quartile, i.e. the median. The crosses represent outliers.