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### Electronic Slide Rule Calculators (1972-1979) The Demise of the Slide Rule Industry With related calculators from the early 80's

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 Texas Instruments (TI) invented the first integrated circuit in 1958, courtesy of TI inventor Jack Kilby, and the hand-held calculator, a prototype called "Cal Tech", invented by TI's Jerry Merryman in 1967. However, the first hand-held calculator with scientific or 'slide rule' functions that was offered to the public was by Hewlett-Packard. The HP-35 was named by Bill Hewlett for the number of keys on the calculator and in 1972 was the beginning of the demise of the slide rule as we know it, Hewlett-Packard announced the HP-35 as a fast, extremely accurate electronic slide rule with a solid-state memory similar to that of a computer. Even though the introductory price was \$395.00, engineers and engineering students flocked to the stores to get these (much like the iPod craze of today). Some students sold their cars to be able to afford one. However, because the exhorbitant manufacturing cost of the HP calculators put them out of reach of 90% of the general populace, the slide rule continued its popularity and usefulness for four more years. In ISRM's opinion, the official date of the death of the slide rule occurred on June 13, 1976 when Texas Instruments introduced the single chip TI-30 scientific slide rule calculator for \$24.95 USD, which was below the cost of a comparable slide rule. There was no cost benefit to new students, technicians and engineers to buy a slide rule anymore, as everyone could afford the TI-30. Video on the HP-35 from Hewlett-Packard

Slide Rule Calculators are defined as electronic calculators having the same functions as found on a Basic slide rule with A,B,C and D scales, minimally a multiply, divide and a square root key. Add in square, inverse (CI scale), and Sin, Cos and Tan trig functions and you have what was on Mannheim slide rules defined in 1850. This differentiates them from the four-function (+,-,x,/) calculators first introduced in 1970. Between 1970 and 1972 there were about 100 models of 4-function 'pocket' (some would be considered portable at least) calculators being manufactured or rebranded for the consumer market. When the slide rule calculator was first developed and made available to the common public in 1972, it was only natural to name these very pricey marvels for the tools they were about to replace.

In the July 1968 The Electronic Engineer, authors Hermann Schmid and David Busch wrote about: "An Electronic Digital Slide Rule - If This Hand-Sized Calculator Ever Becomes Commercial, the Conventional Slide Rule Will Become Another Museum Piece". The article goes on to say: "The Electronic Digital Slide Rule (EDSR) of the future not only will be smaller and easier to operate than the conventional slide rule, but it will also be more accurate.". The slide rule industry should have been paying attention.

What made the portable electronic calculator small enough to be as portable as a slide rule was the inventions of Large Scale Integration (LSI) by Ted Hoff of Intel and Integrated Circuits (ICs) by Jack Kilby of Texas Instruments. LSI/ICs stuffed several thousand transistors and diodes into a small low-power usage package needed for many operations of transendental functions. The Light-Emitting-Diode, so crucial to the miniaturization of the battery powered calculator, was invented in the mid-1960s by the US company Monsanto and marketed together with Hewlett Packard. Subsequent manufacturers of seven-segment displays for electronic calculators included Dialight, Fairchild, Litronix, Motorola and Texas Instruments.

Electronic semi-conductor manufacturers leveraged the 'SLIDE RULE' reference as a way to impart confidence in potential buyers that the new devices would do everything that a slide rule could do, but with more significant figures and automatic decimal point positioning, The advanced scientific slide rules added keys to save key strokes and having to calculate exponents and engineering exponentiation, as well as more memory functions. The cursor on a slide rule is analogous to the Memory keys on a calculator. When shiftable function keys were introduced, with the HP65, the number of functions doubled. You might say this analogous to complex 'duplex' slide rules, which had double the functions of a one-side slide rules.

The two very basic 1976 calculators on the right, a U.S. TI-1270 and a Japanese Canon 8M, both meet the minimum requirements to be a slide rule. The canon has a square root key and memory functions. The TI has square root, square and inverse functions.

Japan, Europe and the Soviet bloc started to produce their own Scientific 'slide rule' calculators (with an 'SR-' prefix) starting in 1976. but were behind in their marketing as compared to HP and TI. Once calculators became ingrained into the mainstream of education and technology for everyday use, the 'SLIDE RULE' tag was dropped in 1976 and 'SCIENTIFIC' or 'ADVANCED PROFESSIONAL CALCULATOR' became the standard model names for these multifunction calculators. Later brochures mentioned 'SLIDE RULE' until the Programmable Versions came out and reference to Personal Computing were being reinforced. By 1978 all conventional slide rules manufacturers were either out of business or switched to making other products than slide rules.

The downside to losing the slide rule, as we knew it, was now one needed to keep his batteries charged (which was found to be difficult in the field with calculators having built-in rechargable batteries). A contemporary slide rule can stay functional for over a century, but calculators can be killed by failed components or corroded batteries within a decade, although there was a period in the 1930's where celluloid was first used for cursors and crumbled within 15 years. Since rechargable NiCad batteries were part of the construction of calculators, users did not remove them when stored, and many calculators became unrepairable. It wasn't until about 1976 that 9V batteries replaced the NiCads in the calculators, followed by button cells when Liquid Crystal displays were introduced.

Secondly, and more importantly, a future generation would become numerically illiterate by losing the art of numeracy which was the empetus of the ISRM , with the support of members the Oughtred Society, to create the Slide Rule Loaner Program for Schools. Most of these specimens, listed in the chronological order of their release to the retail market, have red LED displays (or green Fluorescent displays). Liquid Crystal (LCD) displays appeared in 1979 after the model names went away from using SR, denoting 'Slide Rule', in favor of 'Scientific', with the exception of the TI SR-40-LCD and some green VFD (vacuum fluorescent displays) calculators out of Japan, Taiwan and Hong Kong. This gallery, for the most part, only displays electronic calculators that were marketed as SLIDE RULE CALCULATOR or ELECTRONIC SLIDE RULE or have reference to slide rules in their brochures or manuals. Another exception is the presence of a Square Root key. Texas Instruments held on to the SLIDE RULE tag longer than anyone else and their aggressive marketing lowered prices drastically within 5 years. There were a few Japanese calculator makers who used the SR prefix or suffix to denote a 'Scientific' calculator, but without reference to slide rules. The assumption being is that is why the USA did it in their translation and mimicing of U.S. technology. Other brands used "SR" to denote a 'Scientific' calculator with 'Rechargeable' batteries. I'll make a couple of exceptions and show calculators that when released were significant moments in history, like the 4- function Casio Mini, the first low cost pocket calculator in 1972. Review this collection of Articles on the History of Electronic Calculators at xnumber.com. First off ISRM would like to present the oldest electronic slide rule calculator in the museum, the HP9100A, shown on the right and below.

 Hewlett-Packard 9100A Electronic Slide Rule sn816-004471968 - \$4800.00 (\$33,000 in today's money)
Although far from being a 'pocket' slide rule calculator, the 40 pound (18.1 kg) HP 9100A has the honor of being the very first Hewlett Packard calculator. This powerful desk top, portable calculator was introduced in 1968 and the high price made it so only corporate engineering departments could own one. Many engineers stood in line waiting to use it, in place of their slide rule. Some have called this the 1st personal computer, but it could only be programmed for mathematical operations. Bill Hewlett said, "If we had called it a computer, it would have been rejected by our customers' computer gurus because it didn't look like an IBM. We therefore decided to call it a calculator, and all such nonsense disappeared." The 9100A was the first scientific 'slide rule' calculator by the modern definition (i.e. trig, log/ln, and exponential functions), and was the beginning of Hewlett-Packard's long history of using reverse Polish notation entry on their calculators. The vey first paragraph on their sales brochure (3MB PDF) states:"Oriented to the engineering and scientific professions, the new hp 9100A Calculator contains all of the log, trig, and mathematical functions found on complex engineering slide rules - and more!". What is remarkable about the design, it uses NO integrated circuits, just diodes and transistors. The display is a 4" Cathode Ray Tube (CRT) as was used on their famous oscilliscopes. This unit was donated to ISRM by Alexey Davies, Boulder, Colorado, who obtained this in liquidation from his employer, Bell Telephone Labs (later AT&T).

Compucorp 322G 'Micro' Scientist Electronic Programmable Slide Rule
1971-1975 - \$795 (\$5465 in today's money)

 Mr. HuangISRM Donor
The second important milestone was the development of ICs (Integrated Circuits) by Texas Instruments and made available to VARS (Value Added Re-Sellers). Compucorp designed what I believe to be the first PORTABLE Electronic Slide Rule in their Model 322 Micro Scientist, with advanced slide rule functions, and like the HP 9100A, was programmable.with two 80-step memories. The introduction in their manual states "The Micro Scientist is somewhat larger than a slide rule, but it's far more powerful and accurate than anything else its size." This is one of a "300" series of machines for different purposes. The journal "Electronics", for December 6, 1971, on their introduction, said of this series - "Each machine is "microprogramed" with MOS/LSI logic specifically for each application. ROMs produced by Texas Instruments and AMI to Compucorp specs control the keyboard functions pre-programed by the manufacturer. Groups of calculators bearing family names such as Statistician, Scientist, Accountant, and Treasurer, are thus tailored to the user." Under their own name and also Monroe, Sumlock, and IME, Compucorp Computer Design Corporation (later part of Wyle Laboratories of El Segundo, California) designed, manufactured and sold high specification electronic and hand-held calculators in the U.S.A. during the late 1960s and early 1970s. This 4 lb ruggedized calculator, with a cast aluminum housing, brought the electronic slide rule into the field. Preffered by surveyors. The machines included a battery compartment into which either disposable D-cell batteries, or rechargeable Nickel-Cadmium cells could be installed. An external power-pack provided ability to operate on AC power, as well as serving as a charger if NiCad batteries were installed in the machine. Due to the fragile nature of Nixie tube displays, the display technology used in the 300-series machines changed to the new Burroughs Panaplex II seven-segment planar gas-discharge 10+2 digit display. Calculations had a 13 digit precision. The Panaplex display was more durable, less expensive, and could be made smaller to fit within the confines of a 'handheld' device. More on Compucorp at www.oldcalculatormuseum.com/d-compucorp.html
Donated to ISRM by the Huang Collection.
Note 1: This is an educational historical resource intended for non-commercial use. All rights belong to the respective on-line sources and publications.
Note 2: If a Placard is shown with a specimen, that indicates that model (or an advertisement) will be shown in the physical exhibit along with the supportive images below,
Note 3: Some of the following images and manuals were provided by various contributing websites for the on-line gallery until we acquire our own specimens or scan the manuals and handbooks in the archives. Please support them. If you need a PDF of a manual not scanned yet, let us know and we'll increase the priority to get it in the queue.
Note 4: We are attempting to build exhibits with physical specimens, so if you have one of these, preferably one that you used in your career, and would like to donate it, we'll add your photo and bio and archive it for posterity. It always makes a specimen more interesting to know who used it. Thanks!

Compare slide rule scales with their
corresponding calculator keys

Longivity problems for collectors.

On the Left is KERCS (K&E Rotting Cursor Syndrom) found and on the right, corroded NiCad batteries. Either one can make the specimen worthless, especially with claculators, where metal contacts and traces may be dissolved by chemicals in the battery. Many times Cursores may be swapped from one model to another which is more desirable, and battery packs may be re-built with new batteries if the contacts are intact.

Dispay Types

ISRM would like to thank Joerg Woerner of datamath.org for his contribution of TI calculator photos, ephemera and descriptive text as well as his technical advice. ISRM would like to thank David G. Hicks of hpmuseum.org for his contribution of HP calculator photos, ephemera and descriptive text as well as his technical advice.

ISRM would like to especially thank Scott Reynolds of Vintage Calculators Inc (760-975-9503) for his technical advice in restoring these slide rule calculators and for his generous donation of numerous, and rare, calculators for this gallery and exhibit project.

Additionally we'd like to acknowledge the research, documents and images provided by the websites listed below.

### Calculators Introduced in 1974

 Team Electronics Ad Nov 1974, New Scientist Magazine Nortex-Electronics Ad Nov 1974, Texas Monthly Magazine The Brown And White, Lehigh, University, Bethlehem, PA April 1974 Radio Shack Ad, The Morning Record, Meriden, Connecticutt, Nov14, 1974 Faber-Castell 1975 Ad

### Calculators Introduced in 1975

 Scientific Slide Rule Calculator Comparisons, Feb 1975, New Scientist Magazine Guilford Calculator Centre Ad, Feb 1975, New Scientist Magazine Mountaindene Ltd. Ad, Feb 1975, New Scientist Magazine Cavendish Sales Ad, Nov 1975, New Scientist Magazine Landau Radio Ltd. Ad, Nov 1975, New Scientist Magazine Executive Calculators Ad, Nov 1975, New Scientist Magazine

### Calculators Introduced in 1976

 Commodore CBM Scientifics Oct1976, New Scientist Magazine

### Calculators Introduced in 1977 - The Transition Year

 Commodore Pre-Programmables early 1977

### LCD Calculators Introduced in 1980 and later (The Modern era)

 After 1980, Liquid Crystal Displays became predominant as they used very little power. Several models that began life as 'Slide Rule' Calculators retained that nomenclature in the modern era such as the SR-40-LCD, TI-30-II, and TI-55-II. Others are shown here only because the museum does not know what else to do with them.They were acquired as part of lots that contained the sought after slide rule calculators or found their way here through donations from friends of the museum.

### WANTED! - Other Potential Slide Rule CalculatorsNot shown in Gallery - Donations with biographies of donors (if specimen was a personal calculator) are requested

Note: with SR- or -SR, -ESR or reference in literature to slide rules. Items added to List as discovered.

### Calculators in the ISRM archives

We are trying to obtain all the physical specimens, as shown above, for the permanant ISRM - archives and to be used for public exhibits. If you can help by providing your personal SR calculator it would be appreciated by all who will view it.

50 years of working (1960-2010), Here's all the
math instruments the curator used in his career