Abstract A method proposed by McCuaig and Hutchings to assess the internal readability variation of books using the Fry Readability Formula was empirically tested. In each of sixteen books examined, the McCuaig and Hutchings method was found to consistently underestimate the observed readability variation. An explanation of this underestimation is presented. In addition, the authors of this paper propose a change in the logic of McCuaig and Hutchings’ method which eliminates this underestimation.