Hewlett-Packard HP-21 Handheld Electronic Calculator

Hewlett-Packard HP-21 Handheld Electronic Calculator

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This handheld electronic calculator, relatively small and simple for a calculator sold by Hewlett-Packard, was introduced on February 1, 1975 and sold through 1977. Designed as a successor to the HP-35, it was one a series of calculators of this size that also included the HP-22, HP-25, HP-25C, HP-27, and HP-29C. It has a tan plastic case with a black keyboard and thirty rectangular plastic keys. These include ten digit keys, a decimal point key, a display key (to indicate whether or not the result is to be displayed in scientific notation), and four arithmetic function keys that also serve as memory keys. Above these are the elongated enter key and twelve function keys, each of which can take on two meanings. The change sign/square root of x key, the enter exponent/pi key, and the clear x/clear key are left of the enter key. The function keys above this are for exchange/R(convert to rectangular coordinates), R (roll down)/P (convert to polar coordinates) , exponents/natural logs, storage/logs to the base 10, and recall/powers of ten. The back row of keys includes an inverse/ power key, three trigonometric function keys which also can serve as inverse trigonometric function keys, and a blue shift key. Behind the keyboard are two switches, one on/off and one for shifting between degrees and radians in angular measure. The twelve-digit LED display is behind the switches. A mark on the front edge reads: hp HEWLETT • PACKARD 21.
The reverse side of the calculator has prongs for a power adapter/recharger as well as a battery compartment that holds a frame for two batteries. Stamped above the battery pack is the number: 1711S21227. The first four numbers of the serial number indicate that the calculator was made in the eleventh week of 1977. A tag at the base of the back reads: HEWLETT-PACKARD (/) MADE IN SINGAPORE (/) 2.5 V 500mW.
The calculator is in a brown zippered leather-covered, cloth-lined carrying case. A mark on the front reads: hp HEWLETT• PACKARD.
W.A.C. Mier-Jedrzejowicz, A Guide to HP Handheld Calculators and Computers , Tustin, California: Wilson/Burnett Publishing, 1997, pp. 46–47, 132.
David G. Hicks, The Museum of HP Calculators, http://www.hpmuseum.org/, accessed July, 2014.
Randall Neff and Lynn Tillman, “Three New Pocket Calculators: Smaller, Less Costly, More Powerful,” Hewlett-Packard Journal, November 1975, pp. 2-7, 12. Much of the issue is devoted to the HP-21, HP-22 and HP-25.
Currently not on view
Object Name
electronic calculator
date made
Hewlett-Packard Company
place made
Physical Description
ceramic (display board material)
metal (circuitry material)
plastic (case; keys; switches; zipper material)
leather (carrying case material)
overall in case: 4 cm x 10 cm x 15 cm; 1 9/16 in x 3 15/16 in x 5 29/32 in
out of case: 3 cm x 6.5 cm x 13 cm; 1 3/16 in x 2 9/16 in x 5 1/8 in
ID Number
catalog number
accession number
Credit Line
Gift of John B. Priser
See more items in
Medicine and Science: Computers
Handheld Electronic Calculators
Computers & Business Machines
Data Source
National Museum of American History
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My HP21 indicates a build of 5th week 1975. If these units were released FEB 1st 1975 then I must have one of the first units! Cool!

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