Jeffrey A. Shaffer: How to Create a Secondary Axis in Tableau Without Duplicating Marks
"This topic came up relating to a recent discussion on Twitter, and idea posted by Sam Parsons. The idea he posted is basically that we should have more control and flexibility with the X and Y Axis in Tableau. I completely agree, so please vote for this idea. One of the most frequently used "tricks" in Tableau is to duplicate your pill to make a dual-axis chart. This is a very popular trick, because historically, it was the only way to get two different mark types on the same canvas (see Layering Marks in Tableau which leverages Map Layers as another way to hack additional marks on the canvas - more than two mark types)."
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