LR115 cellulose nitrate films efficiency is strongly dependent on the conditions of etching. In this paper a new method to evaluate a correction factor for this effect is given. The film is scanned with an high-resolution scanner, the diameter of the tracks is measured, and the correction factor is calculated from the average diameter of the tracks. The sensitivity of the film is found to have a linear dependence on the average diameter, and the classical correction, based on the residual thickness, can be substituted by a method based on average track diameter.