In this example the stereochemistry is given by up/down-bonds except at position 4 (C-6 within the drawing) where the two methylgroups are located. From the drawing it is unspecified which methylgroup is in axial or equatorial position respectively, therefore the methylgroups can't be distinguished resulting in a predicted value of 26.5ppm for both of them with a fairly large expectation range of 15.6-34.5ppm. (the methylgroups are numbered C-16 and C-17 within the drawing)
In the second example the missing piece of information is inserted by
defining the axial methylgroup using an up-bond. The other methylgroup
is automatically assigned to the equatorial position leading to a dramatic
improvement of the prediction quality. The estimated values for these methylgroups
differ now by ca. 12ppm caused by 1,3-diaxial interaction as to be expected.