> > If you think it's exaggerating the variation, you are not reading the chart.

> That's true of every instance where a chart is criticized for playing around with the axes scale.

Indeed. The criticism, however, is only apt when the chart's intended audience is likely to have a hard time understanding what that chart is trying to communicate. If you're publishing a bar chart in USA Today and its y-axis doesn't start at zero, yeah, that's a problem.

But the OP's chart that started this whole thread? It's fine. First, the intended audience is HN readers, who can be assumed to be numerically literate. Second, it's a line chart whose y-axis labels make clear what the range of variation is. Third, the data points, themselves, are labeled with their values. Finally, the thrust of the chart, that em-dash usage in HN posts has markedly increased since the widespread adoption of LLMs, is itself also explicitly called out and labeled: "+79% from pre-AI baseline."

If you try to tell me that the author of that chart is trying to mislead HN readers about the growth of em-dash use on HN, I'm going to have a hard time taking your claim seriously.

> Imagine the stock price of a company varied between 50.1 and 50.2 over a week. And I presented it as a chart with the min being 50.09 and max being 50.21, and drew all the variation over a large vertical space.

I have an easy time imagining your chart because that's how stock charts are plotted. That's what the financial community expects. That's how it's done: The y axis is bracketed by the low and high values over the period being charted, perhaps after rounding to the nearest nice value. For example, today's chart for the Russell 2000 Index shows a gain of just 0.30%, similar to the tiny relative volatility in your example. The chart's y axis ranges from 2,695 to 2,715 (https://share.google/oKPQxlmZFsgSVoNOS). It does not start at zero.

If it did start at zero, it would be unsuited for its intended purpose. How would you observe the day's variation on what appeared to be a flat horizontal line at the top of a chart whose y axis ranged from 0 to 3000?

Why do you think the financial world does stock charts the way it does stock charts? Do you think financial analysts don't know how to communicate the day’s movement of a stock to each other?

> And then tried to imply that the stock was volatile. What would be the problem?

The problem would be that your audience, if they were accustomed to reading stock charts, would think you didn't know what you're talking about. Your chart would refute your claims, and anybody accustomed to reading stock charts would know it.

> Let me ask you this. What is the point of this chart (or any similar chart)? Simply presenting a table with all the values would have conveyed all the information - wouldn't you agree?

The point of this chart, like any good chart, is to present the intended information to the intended audience faster and more conveniently than the alternatives. (Do you have any problem with that claim?) And, in this case, I'd say the OP's chart met that standard. Likewise, I'd argue that the typical stock chart, which is bracketed by the stock's low and high values, meets that standard as well.

In both of those examples, you could also communicate the same information in a table, but a table wouldn't be as fast or convenient as a chart, given the expected audiences.