[amenod]

It is however very rare that absolute differences matter; and even when they do, the scale should (often) be fixed. For example the temperatures:

[A: 27.0, B: 29.0, C: 28.0]

versus:

[A: 27.0, B: 27.2, C: 26.9]

If scale is fit to the min and max values, the charts will look the same.

Still, as a rule of thumb, when Y axis doesn't start at 0, the chart is probably misleading. It is very rare that the absolute size of the measured quantity doesn't matter.

[Tyr42]

Yeah, you should graph both starting at 0K right? You wouldn't want to mislead people into thinking somthing at 10C is ten times more hot than something at 1C.

[sandgiant]

Indeed. And if they don't you are probably better off normalizing your axis anyway.