In most but not quite all respects, the two halves, _Computer 1_ and _Computer 2_, can compute independently. The _storing register frames_ hold enough relays to store 30 numbers. The registers for these numbers are named _A, B, C, D_, ···, _M, N, O_ in two groups of 15 each. One group belongs to Computer 1 and the other to Computer 2. In each Computer, the _calculator frames_ hold enough relays for storing two numbers (held in the _X_ and _Y_ registers) and for performing addition, subtraction, multiplication, division, and square root. In each Computer, the _problem frame_ stores the numbers that are read off the problem tape and the table tapes, and the _printer frame_ stores the numbers that are read into the printer. The printer frame also stores indications, for example, the signs of numbers, plus or minus, for purposes of combining them. These frames also hold the relays that control the printer, the problem tape, and the table tapes. Jointly for both Computers, the _position frames_ connect a problem in some problem position to a Computer that becomes idle. For example, one problem may finish in the middle of the night; the machine automatically and unattended switches to another problem position and proceeds with the instructions there contained. A backlog of computing on hand can be stored in two of the problem positions, while the other two control the two Computers. In each Computer, the _routine frames_ hold the relays that make the Computer follow the routine instructions. Jointly for both Computers, the remaining frames—the _control frames_, the _BTL frames_, and the _permanent table frames_—hold the relays that control: the alarms and lights for indicating failures; some circuits called the BTL controls; the tape processor; and the mathematical tables that are permanently wired into the machine. The permanent table frames hold the following mathematical functions (see Supplement 2): _sine_, _cosine_, _antitangent_, _logarithm_, and _antilogarithm_. Storing Numbers can be stored in the machine in the 30 regular storing registers of both Computers together. They can also be stored, at the cost of tying up some machine capacity, in the other registers: the 4 calculator registers, the 2 problem registers, the 2 table registers, and the 2 printer registers. Numbers can also be punched out on tape, in either of the two printers, and later read again from the tape. Labels identifying the numbers can also be punched and read again from the tape. Each register in the machine stores a number in the biquinary notation, as explained above. In programming the machine, after mentioning a register it is necessary—as a part of the scheme for checking—to tell the machine specifically whether to hold the number in the register or to clear it. Addition and Subtraction