variation in tracking performance between different quadrants of a circular scale has been shown to be attributable mainly to ambiguity of display-control relationships on this scale, in that motion of pointer may be viewed as either rotary or translatory. dominant tendency is to view it as rotary, a clockwise control movement being associated with a clockwise pointer movement; but there is a significant secondary tendency to view it as translatory, a clockwise control movement being associated with a displacement of pointer upwards or to right, according to quadrant in which target lies. two tendencies conflict when target is in lower and right-hand quadrants, where performance is consequently poorer. Performance is also affected by position in visual field as such.
It has been verified that a clockwise control movement is expected to send pointer to right on a horizontal linear scale and upward on a vertical linear scale. Performance on horizontal scale is no better than that obtained on circular scale under optimal conditions, but unambiguity of linear scale renders it preferable where erroneous reactions are to be avoided.