ars, I think the position you're taking is a bit strong. The author expressed the relationship between transaction volume and price, to reach a certain daily transaction amount: this implies he's perfectly aware that the relationship isn't linear (a move to twice the transactions at half the price is the same movement, irrespective of the price you're asking at - even though it looks like a larger swing if the basis is larger). But the fact that the shape doesn't show this as nicely as the shape you'd like does, doesn't mean that we can't follow the author's reasoning. Why not drop him a line by email explaining that his post would benefit from logarithmic graphs, since htey show the relationships he's discussing better.