The independent variables are the width of the line in characters (shown on the horizontal axis), and the length of the text in words (the "depth" axis). The dependent variable is the time that the algorithm takes to run, and it's shown on the vertical axis.

The orientation of the graphs doesn't change, but the scale does pretty massively, and seems to indicate the rough efficiency of the algorithm (the time is always in the range of 0.0-1.0 seconds, so it's clear that brute force is many times slower than the more-advanced algorithms).