Abstract: An analysis of Rema's automatic log scaler is presented in this article. It points out that in such kind of scaling system, the time interval for scanning the log shadow by the small rotating mirror on the parabolic reflector is not in proportion to the log diameter which leads to errors in measurement. A formula describing these errors is derived, the magnitude of these errors is calculated, and several methods of diminishing these errors are suggested, A11 of these can be used as references in designing and improving such kind of scaling system.