Recording speed. (a) Whatever the form of the record sheet, the speed recording stylus must normally move in a straight line and at right angles to the direction of travel of the record sheet. However, the movement of the stylus may be curvilinear, provided the following conditions are satisfied: the trace drawn by the stylus must be perpendicular to the average circumference (in the case of sheets in disc form) or to the axis (in the case of sheets in strip form) of the area reserved for speed recording, the ratio between the radius of curvature of the trace drawn by the stylus and the width of the area reserved for speed recording must be not less than 2.4 to 1 whatever the form of the record sheet, the markings on the timescale must cross the recording area in a curve of the same radius as the trace drawn by the stylus. The spaces between the markings on the timescale must represent a period not exceeding one hour.
