This attribute controls the appearance of an annotated
coordinate grid (drawn with the AST_GRID routine) by determining
whether the numerical labels for each axis of a Plot should be
drawn upright or not. It takes a separate value for each
physical axis of a Plot so that, for instance, the setting
"LabelUp(2)=1" specifies that numerical labels for the second
axis should be drawn upright.
If the LabelUp value of a Plot axis is non-zero, it causes
numerical labels for that axis to be plotted upright (i.e. as
normal, horizontal text), otherwise (the default) these labels
rotate to follow the axis to which they apply.