Irma H Gross and Elizabeth Walbert Crandall, Management for Modern Families, Second Edition, Appleton-Century-Crofts, 1963


Analysis of a film consists of charting the elements of motions in terms of therbligs. A motion is a very complex activity, and to study it requires its breakdown into simpler elements. These elements must have identical meanings for different workers. The Gilbreths investigated, classified, and named these elements, calling them by their own name spelled backwards—"therbligs." The term therblig can be used to classify the motions of fingers, arms, hands, or the activity of the body as a whole. In any one situation, however, it must be applied only to one of these, such as arms, and not, for example, sometimes to arms and sometimes to fingers.

Each of the 18 therbligs (the Gilbreths recognized only 17) has its special name, symbol, abbreviation, and color by which shown on a simo-chart. Thus, one of the common therbligs, "grasp," is indicated either by G or a horseshoe shape, indicating a hand open for grasping an object. Some of the symbols are self-explanatory; others need a little interpretation for the uninitiated. The therbligs with their symbols and abbreviations are: