tool to investigate the probabilities of winning while developing his blackjack gaming theory. He used FORTRAN to formulate the equations of his research model. The IBM 704 at the MIT Computation Center was used as the official tracker for the Smithsonian Astrophysical Observatory Operation Moonwatch in the fall of 1957. IBM provided four staff scientists to aid Smithsonian Astrophysical Observatory scientists and mathematicians in the calculation of satellite orbits: Dr. Giampiero Rossoni, Dr. John Greenstadt, Thomas Apple and Richard Hatch. The Los Alamos Scientific Laboratory (LASL) developed an early monitor named SLAM to enable batch processing. Registers The IBM 704 has a 38-bit accumulator, a 36-bit multiplier quotient register, and three 15-bit index registers. The contents of the index registers are subtracted from the base address, so the index registers are also called "decrement registers". All three index registers can participate in an instruction: the 3-bit tag field in the instruction is a bit map specifying which of the registers participate in the operation. However, when more than one index register is selected, then their contents are ORed – not added – together before the decrement takes place. This behavior persisted in later scientific-architecture machines (such as the IBM 709 and IBM 7090) until the IBM 7094. The IBM 7094, introduced in 1962, increased the number of index registers to seven and only selected one at a time; the "or" behavior remains available in a compatibility mode of the IBM 7094. Instruction and data formats There are two instruction formats, referred to as "Type A" and "Type B". Most instructions were of type B. Type A instructions have, in sequence, a 3-bit prefix (instruction code), a 15-bit decrement field, a 3-bit tag field, and a 15-bit address field. There are conditional jump operations based on the values in the index registers specified in the tag field. Some instructions also subtract the decrement field from the contents of the index registers. The implementation requires that the second 2 bits of the instruction code be non-zero, giving a total of six possible type A instructions. One (STR, instruction code binary 101) was not implemented until the IBM 709. Type B instructions have, in sequence, a 12-bit instruction code (with bits 2 and 3 set to 0 to distinguish them from type A instructions), a 2-bit flag field, 4 unused bits, a 3-bit tag field, and a 15-bit address field. Fixed-point numbers are