Hi Grant
Charting does not display all of the points. It does things like average values (like prices) and sum (bin) for things like volumes. I don't have a hard set of rules for when that happens. In general, we display as much data as we can, and start collapsing when we have to. If you think about a minutely test for 4 years, for instance, that's 340,000 data points - no monitor can display that. We've made efforts to make the graphs "true" - no interpolation, no curve fitting, stuff like that. But you shouldn't look at a graph and think that you are seeing all of the data.
As for the second question, about plotting custom variables: we made a design decision to plot it all on one axis. You can plot up to five variables, and there isn't a clean way to plot against five different axes. What you can do is click the word "current_price" in your graph. You'll see that toggles the data on and off the graph, and the axis will redraw. That lets you see your individual custom variables as you see fit.
In the long run, I'm sure we'll add more detailed plotting capabilities. The current implementation has its limitations, as you see, but it solves many of the use cases.
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