In order to operate the machine, the staff required is: one maintenance man; one mathematical engineer; about six girls for punching tape, etc., depending on the number of problems to be handled at the rate of about one problem per week per girl. Unlike any of the other mechanical brains built by the end of 1947, this machine will run unattended. Maintenance The relays in the machine will operate for years with no failure; they have the experience of standard telephone techniques built into them. Under laboratory conditions this type of relay had by 1946 operated successfully much more than 100 million times. The tape feeding and reading equipment in the machine may be maintained by periodic inspection and service. The total number of teletype transmitters in the machine is 38. If one fails, it is easy to plug in a spare. The total power required for the machine is about 28 horsepower. Batteries are furnished so that, if the power supply should be interrupted, the machine can still operate for as long as a half-hour. Cost The cost of production of this machine in the size of 4 problem positions and 2 computers has been roughly estimated as half a million dollars. This cost includes material, manufacture, installation, and testing. No development cost is included in this figure. Instead, the cost of development has been reckoned as squaring with patents and other contributions of the work to the telephone switching art. It is unlikely that the general-purpose relay computer will be manufactured generally. The pressure of orders for telephones, the need to catch up with the backlog of demand, and the development of electronic computers—all indicate that the Bell system will hardly go further with this type of computer. In an emergency, however, the Bell system would probably construct such machines for the government, if requested. In the meantime, many principles first used in the general-purpose relay computer are likely to find applications in telephone system work. In fact, a present major development being pursued in the telephone sections of Bell Laboratories is the application of the computer principles to the automatic computation of telephone bills. Chapter 9 REASONING: THE KALIN-BURKHART LOGICAL-TRUTH CALCULATOR So far we have talked about mechanical brains that are mathematicians. They are fond of numbers; their main work is with numbers; and the other kinds of thinking they do are secondary. We now come to a mechanical brain that is a logician. It is fond of reasoning—logic; its main work is with what is logically true and what is logically false; and it does not handle numbers. This mechanical brain was finished in June 1947. It is called the _Kalin-Burkhart Logical-Truth Calculator_. As its name tells, it calculates _logical truth_. Now what do we mean by that? TRUTH