HP-21

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A HP-21 Taschenrechner HP-21.jpg
A HP-21

The HP-21 was a scientific calculator produced by Hewlett-Packard between 1975 and 1978. [1] It was designed as a replacement for the HP-35, and was one of a set of three calculators, the others being the HP-22 and HP-25, which were similarly built but aimed at different markets. [2]

As with most HP calculators then and now, the HP-21 used RPN entry logic, with a four-level stack. It also had a single user-accessible memory register. As was normal at the time, memory was not preserved on power-down. A physical slider switch toggled between degrees and radians modes, which was an unusual feature. It had a 12-digit LED display, which was less than the 15 digits of the HP-35. Because of these fewer digits the HP-21 (and similar calculators such as the HP-25) could display 10-digit floating point numbers but only an 8-digit mantissa with a 2-digit exponent when scientific notation was used. A shift key provided access to functions whose legends were printed on the fronts of the tall trapezoidal keys.

Its HP development codename was Pumpkin, [3] and it was a member of the Woodstock series. Its US price was $125 in 1975, $80 in 1978. [4]

A version adapted to support an additional backward-facing display manufactured by Educational Calculator Devices named EduCALC 21 GD existed as well. [5]

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References

  1. Hicks, David G. "HP-21". Museum of HP Calculators. Retrieved 2014-07-12.
  2. "Hewlett-Packard Journal, November 1975" (PDF). Hewlett-Packard. November 1975. Archived from the original (PDF) on 2017-06-10. Retrieved 2014-07-12.
  3. van der Sanden, Kees. "The HP-21 (Pumpkin)" . Retrieved 2014-07-12.
  4. Thimet, Tony. "Hewlett Packard HP-21" . Retrieved 2014-07-12.
  5. "The EduCALC". 65 Notes . Vol. 3, no. 2. February–March 1976. p. 8. Archived from the original on 2017-07-04. Retrieved 2022-07-01 via HP Museum.