Q: “Does anyone know a “rule of thumb” about what percentage of sales are lost to the used book market over the life of an edition? In other words, if the adoption rate remains basically static, how do royalty returns typically decline after the edition has been on the market for one year/two years/three years?”

A: Robert Christopherson, author of Geosystems:

“Quick response on used-book impact. With my 3-year revision cycle we do not stay ahead of the used-book sales erosion. Fortunately in my field there is so much dynamic change that such a revision cycle is warranted.