[Usefulness of the sum angle according to Björk (Jarabak)]

The term sumangle (SA) according to Björk has been attributed in the literature to Jarabak. The term was not used by Björk in his original works. Because of the demonstrated relations the sumangle can be deducted from the simplified calculation SA = X + 360 degrees, whereby X is the angle between the reference lines NS-ML. Beside from this fact also the high unreliability of defining the necessary reference points makes the sumangle a questionable measurement of vertical skeletal development. Therefore other trigonometric parameters as for instance the Y-axis are preferable.