I agree it is totally unnecessary in this case, but sometimes truncating the y-axis serves a purpose. Many times it is for stylistic reasons, but also if the tr

I agree it is totally unnecessary in this case, but sometimes truncating the y-axis serves a purpose. Many times it is for stylistic reasons, but also if the trend is more interesting then the scale, e.g. most stock charts truncate the y-axis because people don’t really care how much a stock has dropped relative to the value, but are more interested in the overall trend in the time period and the specific times when the trend reversed (I think, I don’t trade in stocks). It is unnecessary to do that in this case because the scale isn’t that vast and you can easily see the trend on an absolute scale. However, this graph serves the same purpose as—I gather—stock charts do. They are interested in what happened while the trend was downwards, and the specific time at when the trend stopped (or at least halted).