It would be nice to show secondary tick marks as well
as the major / primary ticks. For example, if the
major ticks marks are spaced every 10 units -- 10, 20,
30, etc -- then it would be nice to show smaller tick
marks on a finer scale, such as every 1 unit (or
possibly 2 units). The minor scale could be shown
independantly of the major scale such that the major
tick marks might have axis lines while the minor scale
is shown with ticks only, or the major tick marks might
be labeled and the minor ones unlabeled.
It would also be good to design the minor axis to be
able to handle irregular spacing, as this would be
needed to show secondary tick marks on a logarithmic scale.