[vharuck]

Yes. Charts are communication devices. Any "rules" for charts should be seen like similar "rules" for essays or emails: good advice that almost always gives a satisfactory result when followed. Reliable paths for infrequent authors.

But what matters most in charts is the same thing that matters most with writing: pick one major point and stick to it (if you're really good or can't avoid it, maybe a couple points). This also explains why a lot of dual-axis charts don't work: the author explains two sets of data that aren't even measured on the same scale and then leaves the reader to connect them and understand the meaning of that connection. You can't be sure the reader will end up at the point you wanted to make.

That's not to say a dual-axis chart is always the wrong choice. Just that, if you start making one, stop and ask if there isn't a better way to show the data. Same with pie charts.

[uhoh-itsmaciek]

What's a good discussion of the pros and cons of pie charts?

[vharuck]

Edward Tufte is a great source for learning which types of charts and visual techniques do their job best. I enjoyed his book "The Visual Display of Quantitative Information."

Here's a discussion thread about pie charts on his website (Tufte chimes in a few times): https://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=...