Fig 13 shows time to do one FMM evaluation (Laplace and Helmholtz) versus N. It shows 1 second for 10^6 elements.
how many points? i.e., if plot shows elements (triangles), caption should say how many quad points
what FMM accuracy? often people compare these O(N) plots from one paper to another, and don't realize they are comparing timings for results with different accuracies: always a good idea to state the FMM expansion order and the result's expected digits of accuracy
Fig 13 shows time to do one FMM evaluation (Laplace and Helmholtz) versus N. It shows 1 second for 10^6 elements.