Wang LOCI-2AC Calculator
Logarithmic Calculating Instrument

The Wang LOCI-2 Programmable Calculator was introduced in January 1965, replacing the LOCI-1 that was introduced just four months before. The LOCI-2 has more than 1,000 transistors, no integrated circuits, core memory, and National NL-8421/5092 Nixie Tubes for the display. To dramatically improve the speed of multiplying and dividing it actually added or subtracted logarithms. It supported a printer, Teletype, and punched card reader peripherals.

Our LOCI-2 was shipped as a model 2AC, so it has 16 Storage Registers in core memory and a 1412A Teletype interface. It doesn't have a 1407 Storage Register board because it is a model 2A and has a 1410A 16 Storage Register board instead.

Our LOCI-2. #3026, came from the Wang Connecticut Customer Engineering office. It was used in the late 60’s and early 70’s as a test bed and repair kit for field service engineers. If they couldn’t repair a board in the field the defective board was sent to the Wang home office and exchanged for a functioning one. We also received a salesman's case containing a complete set of spare boards, a card reader, and a complete keyboard.

Numbers are stored in the registers in Binary Coded Decimal format. There is a 1, 2, 4, and an 8 bit for each digit in a number. The decimal value of a digit is the sum of the bits for each weight, e.g. a 9 is stored as a 1 and an 8. Each bit is stored in a flip-flop made from two transistors. Most registers are 10 digits wide, so it takes 2 x 4 x 10 = 80 transistors to make a register.

The boards in this LOCI-2 calculator are:

  1. 1501 Input Decoder Control for the Card Reader and Teletype

  2. 1401A Register Decoder and NIXI Display

  3. 1402A W-Register with Binary Adder

  4. 1403B L-Register with Binary Adder

  5. 1404A Main Timing

  6. 1405A Miscellaneous Shift Pulse and Control

  7. 1406A A-Register with Accumulator, Decimal Counter

  8. 1408A Program and Decrement Counters plus Storage

  9. 1412A Teletype Input and Output Control

  10. 1410A 16 S-Registers Containing 10 Digit Decimal + Sign of Each Register (Core)

The restoration blog is here.

There are a few LOCI-2 calculators left, most in private collections. These are the public ones:

The point-to-point wiring on the bottom of the chassis. The circuit breaker at the bottom right is broken and will need to be replaced. It looks like the capacitor for the +10VDC power supply is installed backwards. It looks cleaner than the one at the left for the NIXI power, so it was probably replaced at some time.

This LOCI-2 belonged to Wang field service and came with a case full of spare boards. The field service people would install known-good boards from the case to repair a customer's calculator. Then they would install the broken board in this LOCI-2 to determine the fault, repair the board, and put the repaired board back in the case. This LOCI-2 came with two punched card reader to load programs. Since this LOCI-2 is a Model 2AC it supports a Teletype as an I/O device using the 1412A board that goes in slot 9.

One of the first programmable electronic calculators, this instrument was announced in 1964 and sold from 1965. It was designed by An Wang (1920-1990) and his associates. Wang, a native of Shanghai, immigrated to the United States after World War II, studied computer science at Harvard University, and worked at the Harvard Computation Laboratory. He started his own business in 1951, producing magnetic core memories and other electronic equipment on order. The LOCI or “logarithmic calculating instrument” was the first product marketed by the company. Two versions of the machine were announced: the LOCI I, which was not programmable, and the LOCI II, which was.

A copy of the LOCI Service Manual is on Bitsavers.

The desktop machine has nine digit keys arranged in an array, as well as a zero bar and a decimal point key. Depressing other keys changes the sign of the number, shifts the decimal point, shifts from the logarithmic to the work register, and shifts from the work to the logarithmic register. Further keys are for arithmetic operations, squares, square roots, inverse squares, inverse square roots, inverse logarithms, and clearance of various registers. To the right are controls for the decrement counter, the program counter, and the operation code. According to company advertising, the machine offers ten-digit precision in addition and subtraction and eight-digit precision in multiplication, division, exponentiation, root extraction, and logarithm comput