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