LOGARITHMIC SCALES ARE useful in many fields. Sound power attenuation, musical pitch, star magnitudes, photographic exposure parameters, hydrogen ion concentration and optical densities are all expressed on logarithmic scales, but how different the usages appear! As each technology satisfied its need in an ad hoc manner, the systems took on various peculiar forms. As a result, the essential equivalence of the forms is not generally recognized and the concepts and terminology are usually treated as special cases.