The Museum of HP Calculators The Museum of HP Calculators
Some HP calculators had manufacturing variations. This page lists relatively obvious changes. Some details like the exact plastic and trim colors, and minor ROM revisions are not listed. This page also doesn't list the many singular oddities that collectors have found such as HP-25s that have continuous memory etc. Most of these are probably the result swaps during repairs.
Some HP calculators made for the European market have the commas and dots reversed as compared to their American counterparts. The 20 series used two different displays with the decimals being either square or triangular. The triangular decimals could be interpreted as either dots or commas and so were sold in both the US and Europe. The 30 series models had a jumper change between European and U.S. comma/point formats. (Many later models can be switched by the user.)
Serial numbers on classic models were printed on stickers applied between the feet or in the battery compartment. 20 series serial numbers were molded/heat stamped into the plastic on the bottom or printed on stickers in the battery compartment. 10C series serial numbers were placed in the same general area but their exact position varies noticeably.
There have been a number of calculators made to celebrate certain anniversaries. The HP-14B and HP-32S were made with gold anniversary logos to celebrate HP's 50th anniversary. Some recent anniversary models are shown in the photo gallery.
The HP-35 underwent many major physical revisions as shown in the HP-35 exhibit.
The early HP-35s had a major ROM bug that caused: 2.02 ln ex to display a result of 2. There was also a bug in the trigonometric functions for certain inputs. Some examples were:
| Function | Buggy | Correct |
|---|---|---|
| ARC SIN 0.0002 | 5.729577893 x 10E-3 | 0.01145916 |
| ARC COS 0.0002 | 89.99427042 | 89.98854 |
| ARC TAN 0.0002 | 5.729577893 x 10E-3 | 0.01145916 |
| ARC TAN 1.00020002 | 45 | 45.00573 |
These bugs were quickly fixed and HP recalled early units for an upgrade.
Like the HP-35, early HP-80s were labeled "Hewlett Packard" with no model number. "80" was added to later models. On early versions, the trim strip above the power switch was a piece of metal. Later versions went back to the vacuum-deposited trim used in other classic models. Like the HP-35 and HP-45, early versions had "On" and "Off" painted in white and later versions were molded.
The HP-45 can be found with "On" and "Off" molded or painted on. Like the HP-80, early versions had a metal strip above the power switch to avoid wear on the silver trim.
These calculators can be found with or without a security cable attachment bracket. The bracket is metal and pivots out from the back right corner.
On some versions, the keypad was metallic and had a smooth finish with metallic gold or silver trim. On other versions the keypad was plastic and the trim was light grey or light brown. The texture of the plastic keypads ranged from smooth to textured/matte.
The 30 series also had two very different construction techniques.
Early HP-41Cs used the same key shape used in the 20 and 30 series. Later HP-41Cs had lower keys with a gentler slope for the front (alpha) label. Later "Halfnut" versions have redesigned and simplified electronics. All HP-41s can be found in Halfnut versions although CVs and CXs are much more common than Cs.
Versions can be found with the HP logo/model number in either highly reflective glossy silver or a matte-finished silver. Later models had painted rather than molded key legends.
Late versions of the HP-11C, 15C and 16C were made with HP-12C keys that were repainted. Some HP-16Cs had HP-12C keys that were first repainted to be HP-15C keys and then repainted to be HP-16C keys.
The HP-12C has undergone numerous small modifications in its long run.
Some versions have the display set deep and others are nearly flush with the top of the calculator.
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