If the curve is to show expenses per unit of output, the head must be placed on the vertical line so that the arrow will point downward. In Fig. 206 no head is placed on the arrow, as fluctuations in a payroll mean nothing unless we know the output of work. An increasing payroll may result either from increasing sales or from inefficient production. A decrease in payroll may result from increased efficiency of production or because sales have fallen off undesirably. Accordingly, no head is placed on the arrow and the curve must be interpreted by conditions other than those shown on the face of the card itself. In general, all curves relating to total money expenditures may trend either up or down, without meaning anything unless other conditions are considered. It is only when we express expenditures as expenditure per unit that we really get a curve for which it is safe to say that we should always desire a downward trend as long as quality is maintained.

The insert page on which Fig. 205 and Fig. 206 are printed is made of an especially high grade of paper. Most paper in use to-day contains sulphite pulp and chemicals which cause more or less rapid deterioration. The paper commonly used becomes brown and brittle within five or ten years, so that records on such paper are likely to be useless in a comparatively short time. The high-grade paper used for record cards as are shown in Fig. 205 and Fig. 206, contains only the finest selected linen stock and is guaranteed absolutely against any deterioration for twenty years. The chief advantage of this paper, however, is that it can be used in card form, yet be transparent enough to allow of blueprinting.