The Museum of HP Calculators
HP-21
The first of the 20 series was essentially an HP-35
in a smaller, less expensive package.
Since the HP-21 had 33% more ROM than the HP-35 it
had room for a few extra features, namely:
- Trig functions in radian mode. (The mode was selected by a slide switch.)
- Display formatting. (DSP # displayed # decimal places in scientific mode.
DSP . # displayed # decimal places in fixed mode.)
- Polar/rectangular conversions.
- Storage arithmetic. This was implemented using special keys
for M+, M-, Mx and M/.
- 10^x.
The HP-21 also implemented other changes that appeared in post
HP-35 calculators. For example, it provided y^x rather
than x^y and the CLR key left the storage register intact.
Picture of HP-21 (~47K)
Manual Available
HP-21 features
Technology and Packaging
Dimensions and Weight
Price: $125
Introduction-Discontinuation: 1975-1978
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Picture of HP-21 (~47K)