It is interesting to notice the students’ persistent invocation of “differences”
between values (“This way we actually achieved a result that appears as if there are
enormous differences”). However, their focus here is on the way these differences
are “blown up” by the scaling effect, rather than on them not being constant, as was
the case earlier when differences were invoked. The importance of their prior
knowledge appears to have been adapted to a new use and for a new purpose. The
differences, which were used to drive the way the students made sense of patterns in
the data, were being successfully used here as a powerful tool to evaluate their
success in designing a graph to visually support a certain claim about a trend in the
data.