machines cannot be run slowly enough to give the required length of exposure. Some of the older machines can be changed at rather slight expense so as to have an extra belt-pulley reduction between the motor and the blue-printing machine itself. The newer types of machine can usually be run slowly enough to give the exposure necessary for this heavy paper. If a new blue-printing machine is to be ordered, however, it is well to make some preliminary tests with the cards.
The cost is not great for blue-printing a whole set of record cards once each month after the last data have been plotted. Blue-print paper of heavy weight should be carried on hand, already sensitized and cut to size, four by six inches and four by twelve inches. The original curve cards, each backed by a sensitized card of the same size, are simply fed into the blue-print machine as rapidly as the operator can put the two cards together in pairs.
There is a tremendous advantage in having all curve records made on a high-grade transparent card so that any card may be duplicated by blue-printing whenever desired. It is impossible for anyone to predict what conditions will come up in the future of a business, and the only safe plan is to install from the start such a curve-record system that any card may be duplicated by blue-printing in future years if desired. It frequently happens that an executive wishes to have a blue print made of a recent year's curve card to compare with the curve card of an earlier year, in order that the blue prints may be mailed to some higher official or to some branch-house manager to point out certain conditions which it would be difficult to describe fully if copies of the curve cards could not be sent. Unless, however, the curves for the earlier years are made on cardboard from which blue prints can be taken, it is impossible afterward to make duplicates of these cards except by hand copying or photographing. In many cases it will be found desirable to take a blue print of every record card once each month, so that blue prints may be sent each department head to show him the exact condition of his department as a guide for the next month.
The space toward the left-hand side of the cards shown in Fig. 205 is for remarks which may be necessary to explain different fluctuations in the curves. In Fig. 206 full circles along the curve show those weeks in which a full holiday reduces the amount of the payroll. In the month of April there was, for this particular plant, a half-holiday on the nineteenth. This is shown by a half circle. At the end of the fiscal year we see in Fig. 206 stars to explain why the curve showed a drop to less than
