I'm sorry if this is the wrong spot to mention this typo, but in the above mentioned section there is a small typo within the config object of the .draw() method... (in the pdf version of the book)
y2axis: {min: -0.15, max: 0.69,
tickFormatter: function(val) {return val+" °C";}}
yaxis: {min: 300, max: 400},
... should have the yaxis and y2axis values switched:
y2axis: {min: 300, max: 400},
yaxis: {min: -0.15, max: 0.69,
tickFormatter: function(val) {return val+" °C";}}
Luckily the source code had the correct configuration, but I was lost for a little when trying to find an error in my code. I'm still fairly new to programming, and very much in the 'noobie-see-noobie-do' phase...
It's possible I have an older copy of the book as well - I recently bought this through a Humble Bundle package- but was unable to find a version history to verify.
Anyway, thank you so much for this book, it's been a pleasure to read and very helpful in my journeys!