I don't think they're committing any subterfuge -- they are a gas price reporting service, driven by data that volunteers report via a mobile app.Is that their usual format fo the graph? Designed to exaggerate fluctuations by having the top and bottom of the vertical scale at the high and low points of the data. Poorly done but probably good for their business.
If you're looking for trends, it doesn't make sense to start the graph at zero.
Further, any sensible numerical analysis would require a logarithmic price axis, not linear. But average human beings wouldn't understand that.
