A golden ratio for line charts with truncated y-axis

https://chezvoila.com/blog/yaxis/

While we hold that bar charts should start at zero, there is no such expectation for line charts. But you’ll always find someone on social media to denounce a “dishonest” line chart that enhances the variations by truncating the y-axis. There is usually ample pushback, but it often leads to the question: Where should it start then?

The bottom third of the plot area should remain empty for a line chart that doesn’t start at zero.

...We need a middle point. A range that is small enough to show variations, but with a starting point that is low enough to avoid the misperception that the data reached zero.