Sales Info (with Graphs!)

I've written and read a fair amount about authorial promotion, what is and isn't effective.  Anyone who's tired of book sales talk can feel free to skip this one, but I figured some of you might appreciate a little raw data to go with the conversation.

This is a graph of the sales for The Stepsister Scheme (purple line) and The Mermaid's Madness (black line).  Stepsister has been selling for just over a year now, and Mermaid has been out for about three months.

The sales data comes from...