"Quarterly" Amazon Stats

I'm at bit tardy on my Amazon sales rank summary -- should've had one out in August.  No matter, here's the graph.  Remember that with sales rank, lower values are better.

In general all Plone books are trending upwards, which is not unexpected considering that the Plone 3 titles are being replaced by Plone 4 ones.  Martin Aspeli's Professional Plone 4 Development tops the chart so to speak with a sales rank of 156K with de Alba close behind.  Plone Live once again is in the basement (at the top of the chart), but that is more likely due to its heavy reliance on non-Amazon sales channels. 

The table of the current titles and their sales ranks are given in the table below.  Of interest this time is the column on sales/yr.  I found a graph that illustrated the approximate Amazon sales rank function, which turns out to be a power law.  A little regression with Open Office Calc gave me an equation of

f(x) = (1.3*10^6) * (x^-1.1)

This equation has numerous potentially huge sources of error, but I thought it would be interesting to toss it out and let the authors themselves reflect on the results.  Please note that these are Amazon-only numbers.  Because most titles are published by Packt, this almost certainly is a small fraction of total sales. 

Amazon Page Rank Stats	November 2011
Title	Author	Sales rank	Sales/yr	Rating
Professional Plone 4 Development	Aspeli	156,335	150	4.50
Plone 3 Intranets	de Alba	192,392	120	4.00
Plone 3 Theming	Williams	704,159	29	5.00
Professional Plone Development: Plone 3	Aspeli	692,760	30	4.67
A User's Guide to Plone 4	Nagle et al.	755,217	27	n/a
The Definitive Guide to Plone (2nd ed)	Delmonte, et al.	984,891	20	1.00
Building Websites with Plone	Cooper	1,050,568	19	3.71
Plone 3 Products Development Cookbook	Giménez & Romero	1,270,629	15	4.00
Practical Plone 3	Knox et al.	1,025,403	19	4.80
The Definitive Guide to Plone (1st ed)	McKay	1,239,686	16	4.14
Plone 3 for Education	Rose	1,722,143	11	4.00
A User's Guide to Plone: Updated for Plone 3	Lotze & Nagle	1,773,374	11	3.00
Plone Content Management Essentials	Meloni	1,801,775	10	3.11
Content Management with Plone: Handbook	Lotze& Theune	1,954,272	10	n/a
Plone 3 Multimedia	Gross	2,833,640	6	3.67
Plone Live	Pelletier	2,886,475	6	4.80

I'd like to find out what actual sales numbers are directly from authors, but only if you don't consider it SBI, "sensitive business information".