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The way I see this accomplished is that I can assign a vertical axis to a data serie. The axis would then scale the values, while currently the chart does all the scaling.
Your are mostly correct in your analysis.
There is already an issue for that (
http://bugs.freepascal.org/view.php?id=13832).
Said issue contains a patch which tries to implement multi-axis support.
I have applied only parts of this patch, since the implementation is, in mu opinion,
not quite general enough.
In particular, it would not allow user to control relative axis ranges.
Still, you may take a look -- maybe this will be enough for you until the
proper support arrives.
Since apparently multi-axis charts is highly requested feature, I am planning
to implement it as soon as I have free time to hack on Lazarus.
The plan is as follows:
1) Currently, TChart works with two coordinate systems: Graph (aka world) coordinates
and Image (aka screen) coordinates. I plan to add third, Axis (or data) coordinates.
2) Axis->Graph conversion should be handled by axis according to its conversion mode,
Graph->Image conversion should be handled by chart according to its zoom factor and viewport offset.
3) So the first task is to abstract out all coordinate transformations into
a pair of functions -- AxisToGraph and GraphToAxis, similar to
existing GraphToImage and ImageToGraph ones. Note that both direct and inverse transformation should be handled.
If you want to help, the above is the (first) patch I would like to receive.
After that, we may proceed further.
Patches should be submitted into the Mantis bug tracker.