A logarithmic Y-Axis makes that really hard to judge.
Come on, we're programmers, get good at math!
Thanks, I'm plenty good at math. The point of a graph is to display information visually -- minimal math should be required.
If what you want is the numbers, then a graph doesn't help you -- use a table instead.
If you wanted to show absolute timings, then I would say a separate graph with time / N on they Y-axis would be the right way to do it -- you could see how the time per operation changed as you increased N.