An interesting trend: Downloads from new IPs of my differential equations notes have not spiked in the last week or two, while the real analysis notes have. See (weekly downloads from new IPs, red is real analysis, blue is diffy qs):
(I wonder if the chart will change when I update the the spreadsheet in google docs in the future … we’ll see. The spike I am talking about is of course for the week ending 9/5/10)
My theory is that the differential equations notes are not used as official book in any course (that’s on a semester system), while the real analysis notes are used as official book somewhere. The diffy qs notes tend to spike a little near time of midterms which seems to imply that people use it for extra reference. Also two (yes that’s two) people have bought the bound copy of the real analysis book in the past month, which triples the volume of sold copies. When I taught with my diffy qs notes, I got 5 sales. If it’s the official book, it seems more likely that someone will still buy a hard copy even if they can download and print the book for free (well given cost of printing and simplest binding, it’s not that much cheaper actually).