It is frequently a great convenience to be able to run through the machines cards for several years back so that comparative statistics may be made. The preservation of the cards makes it unnecessary to dig out the original records. The uniform size of the cards makes it possible to preserve large quantities of them with comparatively little labor.

In punching the cards there are certain holes relating to departments, dates, etc., which are repeated time after time for large numbers

Courlesy of the Tabulating Machine Company

Fig. 230. Hollerith Tabulating Machine for Totalling the Data Contained on Punched Cards

The machine illustrated has four counters, permitting the simultaneous taking off of the data contained under four different headings on the punched card. The sorted cards are placed at the left of the tabulating machine and run through at the rate of about 3,000 per hour. Totals are read from the dials shown at the right

324 GRAPHIC METHODS

of cards. Instead of the operators punching these repeated holes one by one in each card, the cards are punched by a gang punch, which at a single stroke punches several holes in many different cards. The gang punch can be seen in Fig. 231 on a table near the right-hand side of the illustration.

Manufacturing companies now use the tabulating machines for keeping track of the cost of different orders and of different classes of work in the factory. The data from the original time slips of the workmen are transferred by the punching machines to the cards day by day as the time slips are turned in. The punched cards can then be sorted by order number and department, so that when each order is completed the total cost of all work on that order is obtained. The distribution of the value of work done by different departments can be had also if desired.