IBM Field Engineer's Hexadecimal Adder

Hex Calc front 300pxA manual calculator for hexadecimal numbers.

Dates: First appeared 1957
Donated: 2009 via Noel Cox
HoCC Number:   



The device does simple addition and subtraction of hexadecimal numbers (numbers in base 16). The dials can be turned using a stylus stored in the bottom right-hand corner of the device.

IBM engineers maintaining the IBM System/360 range of computers used hexadecimal adders.  The IBM 360 series popularized the use of 4-bit hexadecimal numbers as a method for making short representations of long binary numbers, which were needed for addresses in memory.

Engineers investigating software problems for the operating system and application programs used the calculator to calculate addresses in memory. System/360 used truncated addressing, in which instructions do not contain complete addresses, but rather specify a base register and a positive offset or displacement from the address held in the base register. To find an address the offset was added to the base address. Contemporary programmers were used to direct addressability of any memory cell and so not being able to know by looking at an instruction where its data are located was considered inconvenient.  Truncated addressing was suitable for the design of System/360 since its instructions were common to a series of machines with significantly different specifications.

The invention of the hexadecimal adder is attributed to an IBM programmer, Carl J Lombardi. In the 1960s, he made a wooden prototype at home. He used this to demonstrate his design to colleagues at IBM and to the Sterling Plastics Company, who were later given the contract to make the calculator.

George and Mary Staab operated Sterling Plastics in Mountainside, New Jersey. The company created a range of mathematical instruments. Sterling had created a popular decimal calculator, similar to the hex calculator, the Dial-A-Matic. A patent for the calculator is US Patent 2,797,047 (filed April 30, 1954; published June 25, 1957). Sterling Plastics bought the Acu-Rule Manufacturing Company in 1968, an important slide rule company founded in 1938. In 1970 Sterling Plastics was sold to Borden Chemical; the last products appeared in 1972.

J V Tucker


Additional Information

1957 US Patent: ( US Patent 2797047 )

The International Slide Rule Museum has a wealth of material on products and manufacturers, including Sterling and Acu-Rule

About Hexadecimal Numbers