sales rank

I've toyed around in the past with ways to use the Amazon sales rank tracker to estimate the sales numbers for How to Teach Physics to Your Dog. It's geeky fun, but not especially quantitative. Yesterday, though, I found a reason to re-visit the topic: calibration data! OK, "calibration data" is probably too strong a description. "Calibration anecdote" is more accurate. Yesterday when I went into work a little after 10, a comment somebody made sent me to the actual Amazon page for the book, where I saw a little note next to the price information saying "Only 5 left (more are coming)-- order…