I've read in several places that story points are not necessarily linear.
i.e., an "8 point" task is not the same as two 4 point tasks and so on.
I totally get the argument about these being an indication of complexity rather than time taken.
But if they're not a linear scale, then how can you do arithmetic on them? If an 8 story point takes, say, 3 times longer than 2 x 4 story points, then how do burndown charts work from an arithmetic point of view?
If our velocity is, say, 30 a sprint then this means we could do 30 x 1 story point features. But these might be, 30 half an hour jobs. Equally if it was 2 x 15 story point features, these are probably monster tasks which seems equally unlikely.
Perhaps I am wrong in my assertion that they are non-linear?
Or can anyone explain this to me?