The value axis can now go on the left side (as before), the right side
or both sides of column, stacked column, line, area and scatter graphs:
https://helpx.adobe.com/illustrator/desktop/automate-visualize-data/visualize-data/change-graph-value-axes.html
With the axis on both sides, Separate Scales gives the series assigned
to the right axis a scale of their own there, with its own tick values
(rightTicks, rightAxisMin, rightAxisMax):
https://helpx.adobe.com/illustrator/desktop/automate-visualize-data/visualize-data/assign-different-scales-to-value-axes.html
- A series goes on an axis with Group Selection (or `seriesIndexes`)
and `valueAxis` left or right. Without separate scales both sides
show the one scale.
- Each axis stacks its own stacked columns and areas; stacked columns
of the two axes take a slot of the cluster each instead of covering
each other.
- An axis with no series of its own shows the other one's scale. The
right scale's zero gets a line of its own when it isn't the left's.
- The right axis' labels push the legend further right.
- With series on both axes picked, the Graph Type query returns no
value axis, so the dialog's OK leaves each series where it is.
- Graph Data drops right-axis assignments for series the new data no
longer has.
Own choices, as the pages don't say: bar graphs keep their value axis
along the bottom, and scatter graphs draw every series on one scale.
New fields (valueAxis, separateScales, rightSeries, rightTicks,
rightAxisMin, rightAxisMax) are written only when set, so other files
are unchanged and older versions draw the left axis as before. Graphs
with the axis on the left draw the same art as before.