HP-35 RED DOT

HP-35 Version 1- Red Dot

The HP-35 was HP's first pocket calculator. It was introduced in 1972 when most calculators (including expensive desktop models) had only the four basic functions.The HP-35 was the first pocket calculator with transcendental functions and the first with RPN, Reverse Polish notation. During the production process, the revolutionary HP-35 was slightly modified developing to four distinct versions. The first HP-35 (version 1) was the earliest and only production version that reveals a red dot to the right of the power switch when turned on. Another Red Dot characteristic is the serial number label placed between the 2 lower pads on the back of the calculator. The serial number should be typed into a narrow silver region. All but three HP 35 Red Dots in this table have this feature. Two of the different ones (S/N 1143A 03288 and 1230A 89591) have several other features from higher versions, therefore there were either substantially repaired or rebuilt from spare parts. The third one 1143A 01097 was twice returned to HP for service.
The HP 35 Red Dot version is very rare. Most of them are in the hands of calculator collectors already.
Now that you know where the serial number is, check the number. With few exceptions, the number will read 1143A XXXXX. The highest recorded serial number on an authentic Red Dot is 1143A 04280. From the collected data in this table, it follows that the total number of HP-35 Red Dots is in the range of 4200-4500. The last Red Dots were produced concurrently with very early versions 2. Therefore, the exact count is not possible to determine. There exist a few HP-35's, which have Red Dot S/N, but in fact are versions 2 or higher.Those calculators changed from Red Dot to version 2 during an HP service repair. Some very early versions 2 with Red Dot serial number could be produced as versions 2, such as 1143A 04196 in this table. Some of the Red Dots represented on this table may not have the 2.02 ln e^x ROM Bug. They were recalled by Hewlett Packard who guaranteed repair after the Bug discovery
Recently, another extremely rare Big Bug has been discovered in some very early Red Dots! That bug exists in some HP 35 prototypes such as Dean Winter's prototype.

In this database are listed most of known and still existing HP 35 Red Dots.

The Bug

The first HP-35s had a famous Bug in the ROM IC. But not only the HP 35 Version 1 had that buggy ROM, there were produced more than 20000 such units, most of them were version 1 and version 2. Hewlett Packard company offered a free replacement of those ROMs and many owners used that possibility.

For example 2.02 ln e^x display a result of 2. There was also a bug in the trigonometric functions for certain inputs. Below are presented some of the bugs.

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

There exists an another extremely rare Big Bug, which was not known until recently. This bug was fixed very early, so even most Red Dots don't have this bug in their ROMs. In fact, less than five such HP 35s are known today. There could exist a possibility, that this buggy ROM was accidentaly inserted to a HP 35, so your HP 35 might have this bug, too.
You could test for the bug by the sequence

1 eex chs 10 ln

and if the bug was present, then you'd receive an erroneous answer differing from the correct result by hunderts of percents. Therefore "Big Bug" :-)

Function		Big Bug		Correct
1 eex chs 10 ln		-123.0258509		-23.02585093

Acknowledgements:
Robert Benson, Ignazio Cara, Tom Drewski, Rudolf Maximilian Foerste, John R. Galie, Massimo Gnerucci, Wlodek Mier-Jedrzejowicz, Adam Jones, Claus Possberg, David Ramsey, Paolo Reda, Scott Reynolds, Ed Sternby, Katherine Wasserman, Dean Winter

Last update: 20. November 2024

Email: ecksteinm(at)volny.cz

2006-2024 (C) Michael Eckstein

HP is a trademark of the Hewlett-Packard Company.

Serial Number	Reference	Owner	Images Click to resize	the Bug	Big Bug	Functionality	Comment
1143A 00037	Dean Winter	Dean Winter		No	No	OK	Version 2. Only the back cover is from the HP 35 Red Dot. The serial number is hard to read, but has been thoroughly researched by the owner and Scott Reynolds, who also took a picture of the serial number.
1143A 00051	Nicolas Recalde	Nicolas Recalde		Yes	Yes	OK	This Red Dot has the Big Bug
1143A 00054	Bill McNeil			Yes	No	OK	Version 2. This HP 35 has NOT the Big Bug, despite it has the Bug. The back instruction label is a newer version and the front was replaced during a repair of the switch in Cupertino.
1143A 00065	Tom Terry	Tom Terry		Yes	Yes	OK	This Red Dot has the Big Bugand all other bugs except the fourth one listed below. It has a name plate personalized with a name of a member of the HP 35 design team.
1143A 00100	Michael Eckstein			Yes	Yes	OK	This Red Dot has the Big Bug Back side with labels is from a newer version. S/N label was replaced by a substitute and placed in the battery compartment during some repair in a HP service. There exist an another HP 35 without any bug and not Red Dot, but has the original back side of this RD and has the correct S/N label 1143A00100.
1143A 00122	Vincent Lextrait	Vincent Lextrait		No	No	OK
1143A 00159	John R. Galie			No	No	OK	Version 4!
1143A 00357				Yes	Yes	OK	This Red Dot has the Big Bug
1143A 00364	Adam Jones	Adam Jones		?	?	?	Version 4!
1143A 00403	Tom Drewski			No	No	OK
1143A 00423	Ken Chuck	Ken Chuck		No	No	OK
1143A 00429	Wlodek Mier-Jedrzejowicz	Wlodek Mier-Jedrzejowicz		?	?	?
1143A 00491				Yes	Yes	OK
1143A 00516	Jon Bremner	Jon Bremner		Yes	?	OK
1143A 00563	Andreas Müller	Andreas Müller		No	No	OK	Unfortunately, this Red Dot was "repaired"on May 4, 1973 at HP - meaning it got the updated mainboard without bugs. The instruction label was replaced by a newer type.
1143A 00667	Joaquim Compte	Joaquim Compte		Yes	No	OK
1143A 00700	Borislav Agapiev	Borislav Agapiev		Yes	Yes	OK	This Red Dot has the Big Bug.
1143A 00754	Albert Threlfall			Yes	Yes	OK	This Red Dot has the Big Bug. No Red Dot with the Big Bug was found after this S/N
1143A 00801	Eric Hall	Eric Hall		Yes	No	OK
1143A 00840	Scott Reynolds			Yes	No	OK
1143A 00882				No	No	OK
1143A 00944	Dean Winter	Dean Winter		Yes	No	OK	Version 2
1143A 00957	Tom Drewski	David J		Yes	No	OK
1143A 00975	Dean Winter	Dean Winter		Yes	No	OK	The Red Dot switch has no red on it.
1143A 01003	Scott Reynolds			No	No	OK	The Red Dot switch has no red on it. The back label is from the newer version. This HP 35 has other parts from a newer version possibly replaced during The Bug repair.
1143A 01011	Borislav Agapiev	Borislav Agapiev		No	No	OK
1143A 01045	John R. Galie			Yes	No	OK
1143A 01062	Rudolf Maximilian Foerste	Rudolf Maximilian Foerste		Yes	No	OK	ARC key not functioning
1143A 01097	Chris Bennett	Chris Bennett		No	No	OK	The back instruction label is from the newer version. Original back S/N label was also removed and replaced by a newer one during one of two repairs of the calculator in a service.
1143A 01149	Scott Reynolds			No	No	OK
1143A 01173				No	No	OK
1143A 01233	Scott Reynolds			No	No	OK	The Red Dot switch has no red on it. The front and the back labels are from the newer version. Labels were probably replaced during a repair of the switch or ROM replacement in a service.
1143A 01257				No	No	OK	The Red Dot switch has no red on it. The back label is from the newer version. The label was probably replaced during a repair of the switch or ROM replacement in a service.
1143A 01279	Tom Drewski	Luis S		Yes	No	OK
1143A 01469	Vincent Lextrait	Vincent Lextrait		Yes	No	OK
1143A 01563	John R. Galie	John R. Galie		Yes	No	OK
1143A 01640				Yes	No	OK
1143A 01660	Katherine Wasserman	Katherine Wasserman		No	No	OK
1143A 01723	Michael Eckstein			Yes	No	OK	The back instruction label is from a newer version.
1143A 01743						NO
1143A 01873	Tom Drewski			Yes	No	OK
1143A 02069	Mike Morrow	Mike Morrow		No	No	OK	This Red Dot was traded for a new TI 58 in 1977
1143A 02141	Paulo Roberto Alves	Paulo Roberto Alves		Yes	No	OK
1143A 02198	Michael Eckstein			Yes	No	OK
1143A 02201?	Eric Hall	Eric Hall		Yes	No	OK	Eric Hall: 02251 is the serial number that the seller provided. It looks to me like it could be 02201 — the second to the last number is almost impossible to see, and others are very faint.
1143A 02251	James Linder	James Linder		Yes	No	OK
1143A 02282	Ed Sternby	Ed Sternby		Yes	No	OK
1143A 02313				Yes	No	OK
1143A 02338	Scott Reynolds			No	No	OK
1143A 02369	Tom Drewski	Tom Drewski		Yes	No	OK
1143A 02373	Tom Drewski	Tom Drewski		No	No	OK	Version 3
1143A 02461				Yes	No	OK
1143A 02499	Alberto Fenini	Alberto Fenini		Yes	No	OK
1143A 02501	Reinhard Hawel	Reinhard Hawel		No	No	OK
1143A 02581	Scott Reynolds			No	No	OK
1143A 02585	Paolo Reda	Paolo Reda		Yes	No	OK
1143A 02662				No	No	OK	This unit has a name plate personalized with a name of a member of the HP 35 design team.
1143A 02736	Scott Reynolds			Yes	No	OK
1143A 02741	Paul A. Grace			Yes	No	OK	Version 2, no sign of any service repair!
1143A 02816	Dean Winter	Dean Winter		No	No	OK
1143A 02832	Romeo Froicu	Romeo Froicu		Yes	No	OK
1143A 02852	Tom Drewski	Tom Drewski		Yes	No	OK
1143A 02860	Peter Keenan	Peter Keenan		No	No	OK
1143A 02874	Ignazio Cara	Ignazio Cara		No	No	OK
1143A 02967	Bob Wolfson	Bob Wolfson		Yes	No	OK
1143A 03007					No	No
1143A 03048				Yes	No	OK	The Red Dot switch has no red on it. The back label is from the newer version. The label was probably replaced during a repair of the switch in a service.
1143A 03102	Tom Drewski	Mark H		No	No	NO	Version2
1143A 03153	David Ramsey	David Ramsey		No	No	OK
1143A 03179	Michael Eckstein			Yes	No	OK
1143A 03212	Borislav Agapiev	Borislav Agapiev		Yes	No	OK
1143A 03216	Derek Rowe	Derek Rowe		Yes	No	OK
1143A 0324X	Massimo Gnerucci	Massimo Gnerucci		Yes	No	OK
1143A 03288	Wlodek Mier-Jedrzejowicz	Wlodek Mier-Jedrzejowicz					This HP 35 RD has been repaired. The label at the front says HEWLETT PACKARD 35. The label with the number has bigger numeric digits, and the silver area of the label is higher from top to bottom than on all the others.
1143A 03441	C. David Turner	C. David Turner		Yes	No	OK
1143A 03541				No	No	OK
1143A 03711	Robert Ross Brown Jr.	Robert Ross Brown Jr.		Yes	No	OK
1143A 03719	C. David Turner	C. David Turner		Yes	No	OK
1143A 03770
1143A 03779	Michael Dietz	Michael Dietz		No	No	OK
1143A 03788	Ignacio Sánchez-Reig	Ignacio Sánchez-Reig		Yes	No	OK	All papers are in Spanish (user manual, accessories list…) but specially a “list of bugs” (also in Spanish)
1143A 03874	Didier Lachieze	Didier Lachieze		Yes	No	OK
1143A 03935	Hans Bloemen	Hans Bloemen				No
1143A 04017	Dr. Kam Fan Sin	Dr. Kam Fan Sin		Yes	No	OK
1143A 04161 ?						OK	Serial number was guessed from the image.
1143A 04196	Adam Jones	Adam Jones		Yes	No	OK	This is the version 2 with the Red Dot serial number label. This calculator is in an original state, contrary to the other Versions 2 with lower S/N. One known Red Dot with a higher serial number is known. From that follows that some of Red Dots were made concurrently with very early HP 35 versions 2
1143A 04253	Marcel Soklaski	Marcel Soklaski		Yes	No	OK	This is the version 2 with the Red Dot serial number label. This calculator is in an original state.
1143A 04281	Michael de Estrada	Michael de Estrada		Yes	No	OK	This is an original Red Dot with the highest S/N known sofar.
1143A 04313	Scott Reynolds			Yes	No	OK
1143A 04921	Scott Reynolds			Yes	No	OK	This is the version 2 with the Red Dot serial number label. This calculator is in an original state and has the highest Red Dot type serial number kown.
1143A 05141	Pierre P.	Pierre P.		Yes	No	OK	This is the Red Dot with the version 2 serial number label.
1143A 05295						NO	Version 2 This calculator is in an original state, The label with the number has bigger numeric digits, and the silver area of the label is higher.
1230A 89591	Claus Possberg	Claus Possberg		Yes	No	OK	The serial number is not the Red Dot one. The istruction label is from the newer version. The serial number label is from the newer version. The lower back label is missing. The back power connector is from a newer version.