Is 70 twice 60? No, but it looks like it is when the x-axis starts at 50.
However, when you start the axis at 0, the differences between the differences seem very small, while they are what is interesting. That is why this graph start at a different value: the author isn't interested in the absolute numbers: he's interested in the differences from a baseline. Now he could have shown a graph where '0' was the average and plot all the differences, but then many more people would have become confused. Instead he choose the '50' as a baseline, arbitrarily.
Both you and the grandparent are completely wrong in acting all indignant that someone would display a graph like this, when it is a well accepted way to draw attention to the aspects that matter. If I started such a graph at 0, my thesis advisor would rhetorically ask me "What are you trying to convey here?".
From any graph, you can draw right and wrong conclusions. You insist that this graph is wrong because the simplest conclusion you can draw from it is wrong. Well, that's not the fault of the graph: that is the fault of you trying to interpret the graph in an overly naive way, without considering the point of the graph.
The differences between 70 and 60 is not that small (~15%).
There are many ways you can use chart's to try and mislead people, but when you need to do that it's a sign that you are trying to suggest something that's not true.
PS: The first words out of a competent thesis advisory when looking at those charts would be "where are the error bars?"
But the data we're dealing with here isn't on the order of a few percentage points. The values range from about 45-85 on most of them, which is plenty large enough to see given a full range from 0-100. And there's absolutely no reason to use three different scales for four different graphs when the data on all of them is in roughly the same range.
I'm not insisting that the graphs are wrong. I'm saying that they're done badly because they're confusing and make it very easy to draw incorrect conclusions about the data.
Both you and the grandparent are completely wrong in acting all indignant that someone would display a graph like this, when it is a well accepted way to draw attention to the aspects that matter. If I started such a graph at 0, my thesis advisor would rhetorically ask me "What are you trying to convey here?".
From any graph, you can draw right and wrong conclusions. You insist that this graph is wrong because the simplest conclusion you can draw from it is wrong. Well, that's not the fault of the graph: that is the fault of you trying to interpret the graph in an overly naive way, without considering the point of the graph.