A punch-card machine that may have a fairly large amount of internal memory, perhaps 30 or 40 registers where numbers or words may be stored and referred to. SPEED The speed of various operations with present IBM punch-card machines is about as shown in the table. MACHINE OPERATION TIME IN SECONDS Key punch Punch 80 columns About 20 to 40 Verifier Check 80 columns About 20 to 40 Sorter Sort 1 card on 1 column 0.15 Interpreter Print 1 line 0.8 Reproducer Reproduce a card, all 80 columns 0.6 Collator Merge 2 cards 0.25 Multiplying punch Multiply by 8 digits 5.6 Calculating punch Add 0.3 Calculating punch Multiply by 8 digits 3.6 Calculating punch Divide, obtaining 8 quotient digits 9.0 Tabulator Print 1 line, numbers only 0.4 Tabulator Print 1 line, letters included 0.75 Tabulator Add numbers from 1 card 0.4 COST Punch-card machines may be either rented or purchased from some manufacturers but only rented from others. If we take the cost of a clerk as $120 to $150 a month, the monthly rent of most punch-card machines ranges from ⅒ of the cost of a clerk for the simplest type of machine, such as a key punch, to 3 times the cost of a clerk for a complicated and versatile type of machine, such as a tabulator with many attachments. The rental basis is naturally convenient for many kinds of jobs. RELIABILITY The reliability of work with punch cards and punch-card machines is often much better than 99 per cent: in 10,000 operations, failures should be less than 2 or 3. This is, of course, much better than with clerical operations. There are a number of causes for machine or card failures. Sometimes cards may be warped and may not feed into the machines properly. Or, the air in the room may be very dry, and static electricity may make the cards stick together. Or, the air may be too humid; the cards may swell slightly and may jam in the machine. A punch may get slightly out of true alignment, and punches in the cards may be slightly off. A relay may get dust on its contact points and, from time to time, fail to perform in the right way. Considerable engineering effort has been put into remedying these and other troubles, with much success.