None of these comments, however, are criticisms of the machine. Instead they show avenues of development for future machines. As was said before, for solving most differential equations, this machine has no equal to date. The range of problems which any differential analyzer can do depends mostly on the number of its integrators. The second differential analyzer has 18 and provides for expansion to 30. The machine is constructed, also, so that it can be operated in 3 independent sections, each working to solve a different problem. The differential analyzer can operate unattended. After it has been set up and the first few results examined, it can be left alone to grind out large blocks of answers. An interesting example of the experimental use of a differential analyzer in a commercial business is the following: In Great Britain, R. E. Beard of the Pearl Assurance Company built a differential analyzer with 6 integrators. He applied this machine to compute to 3 figures certain insurance values known as _continuous annuities_ and _continuous contingent insurances_. He has described the machine and the application he made in a paper published in the _Journal of the Institute of Actuaries_, Vol. 71, 1942, pp. 193-227. Chapter 6 ACCURACY TO 23 DIGITS: HARVARD’S IBM AUTOMATIC SEQUENCE-CONTROLLED CALCULATOR One of the first giant brains to be finished was the machine in the Computation Laboratory at Harvard University called the _IBM Automatic Sequence-Controlled Calculator_. This great mechanical brain started work in April 1944 and has been running 24 hours a day almost all the time ever since. It has produced quantities of information for the United States Navy. Although many problems that have been placed on it have been classified by the Navy as confidential, the machine itself is fully public. The way it was working on Sept. 1, 1945, has been thoroughly described in a 540-page book published in 1946, Volume I of the Annals of the Harvard Computation Laboratory, entitled _Manual of Operation of the Automatic Sequence-Controlled Calculator_. Since then the machine has been improved in many ways. This machine does thousands of calculating steps, one after another, according to a scheme fixed ahead of time. This property is what gives the machine its name: _automatic_, since the individual operations are automatic, once the punched tape fixing the chain of operations has been put on the machine, and _sequence-controlled_, since control over the sequence of its operations has been built into the machine. ORIGIN AND DEVELOPMENT