[Kampar]

>>just use the rotate, canvas, arbitrary

Yep - you could do that too. But even in the method in the tutorial you don't have to type the rotation angle in, the measure tool still puts it in automatically for you you just have to change the plus/minus sign. So its a question of which route you prefer to get the rotation done!

[Edit] - actually, thinking about this more, maybe the reason I do it this way is that I sometimes use the same method in a layered file and you only want to rotate the one layer rather than the entire canvas. So I guess it's too difficult for me to remember two different ways of doing this!

CR also has a nice trick where instead of duplicating the background layer you just turn it into a normal layer and rotate it ... but it was easier for me here just to say duplicate layer (as you're going to throw the file away later anyway!)