Digitrex MCK-8 Handheld Electronic Calculator

This small, chunky four-function calculator has fifteen square plastic keys, zero and decimal point bars, and rectangular on and constant (K) keys. In addition to digit and arithmetic function keys, there are clear and clear entry keys. The subtraction key serves as a difference key and the plus key as a total key. At the back is an eight-digit LED display. A tag next to the display reads: Digi (/) trex.
A sticker on the back of the case reads: MCK8 OPERATING INSTRUCTIONS. A sticker atop this reads: MADE IN U. S. A. – FO[. . .] (/) CIMATRON Co. (/) by R B. M. [sic] Corp. (/) Serial #MCK-8 403565. A socket at the top allows for recharging the batteries.
The leather-covered, velvet-lined case for the calculator is like a jewelry box.
Compare Hapco Porta Mark II.
Digitrex sold a desktop printing electronic calculator in 1974. R.B.M. Corporation, a firm in Arlington, Texas, sold the Scientific calculator around 1973.
Guy Ball and Bruce Flamm, The Complete Collector’s Guide to Pocket Calculators, Tustin, CA: Wilson/Barnett, 1997, p. 68.
The Vintage Calculators website describes the Hapco Porta Mark II, RBM Scientific.
Los Angeles Times, January 22, 1974, p. B4.
Currently not on view
Object Name
electronic calculator
date made
Physical Description
metal (keyboard; tag; circuitry; case trim material)
plastic (case; keys; display cover material)
paper (sticker material)
leather (case cover material)
cloth (case lining material)
overall: 1 1/8 in x 3 in x 4 in; 2.8575 cm x 7.62 cm x 10.16 cm
place made
United States: Texas, Arlington
ID Number
catalog number
accession number
See more items in
Medicine and Science: Computers
Handheld Electronic Calculators
Computers & Business Machines
Data Source
National Museum of American History, Kenneth E. Behring Center


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