How do Amazon charts work anyway?

I’ll never understand the vagaries of Amazon sales. esterday and for the last few weeks, ATOF had been slowly slipping down the charts–the doldrums of summer, I thought, with no orders from universities for their classes, no press attention, and so on.

Today, it’s in the 3500’s on the charts, and the #12 bestseller in the computer and video games section.

I am told that Tim O’Reilly has a mystical formula that he can use to determine sales figures with exactitude based on Amazon sales rank data. From where I sit, it’s gotta be a heck of a formula, and probably involves eye of newt.