My point is they are shifting the data arbitrarily. The Thordon data points are lower than both the Kelburn and Airport data points for the following reason: "Thorndon (closed 31 Dec 1927) has no overlap with Kelburn (opened 1 Jan 1928). For the purpose of illustration, we have applied the same offset to Thorndon as was calculated for the Airport." - i.e. they shifted it down as much as the Airport even though the Airport has a higher average temperature
The data isn't being "shifted", and it's not arbitrary. Again, the graphs are being used to illustrate changes in temperature, not actual temperatures. And, again, this is a very simple analytical tactic.
This is not unlike a non-programmer being skeptical of Quicksort because it's "arbitrarily dividing data".
