A friend who's been published in the trade presses continuously since the early 1970s has written to say "A quick review indicates that a factor of 6 to 8 would be about right. I'd have to check my royalty statements to get an exact fix..."
He's talking about the factor used to multiply Ingram's sales figures to get the total (non-Ingram + Ingram) sales count. In our series on book sales, I've been multiplying the Ingram sales figure by six; know that this may be a little low and multiply by seven if you wish.
(This note will be added to the publishing overview posting.)