Milestones:First Practical Field Emission Electron Microscope, 1972 and Milestones:Development of the HP-35, the First Handheld Scientific Calculator, 1972: Difference between pages

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== First Practical Field Emission Electron Microscope, 1972  ==
== Development of the HP-35, the First Handheld Scientific Calculator, 1972  ==


''Hitachi developed practical field emission electron source technology in collaboration with Albert Crewe of the University of Chicago, and commercialized the world’s first field emission scanning electron microscope in 1972. This technology enabled stable and reliable ultrahigh resolution imaging with easy operation. Field emission electron microscopes have made invaluable contributions to the progress of science, technology and industry in physics, biology, materials, and semiconductor devices.'' [[Image:Hitachi 1972 FE-SEM HFS-2.jpg|thumb|right|Photo 1: Hitachi's Wolrd First Commercial FE-SEM (model HFS-2), 1972]][[Image:Crewe 1972 T2-bacteriophages.jpg|thumb|right|Photo 2a: Observation of T2-bacteriophages, Prof. A. V. Crewe, 1972, Equipment: HFS-2 FE-SEM]][[Image:Tanaka 1984 T2-bacteriophages.jpg|thumb|right|Photo 2b: Observation of T2-bacteriophages, Prof. K. Tanaka (Tottori University), 1988, Equipment: in-lens type FE-SEM]][[Image:Tonomura 1984 AB-Effect.jpg|thumb|right|Photo 3: Experimental Evidence for Aharonov-Bohm Effect by Electron Holography, Tonomura, 1986]]
''The HP-35 was the first handheld calculator to perform transcendental functions (such as trigonometric, logarithmic and exponential functions). Most contemporary calculators could only perform the four basic operations – addition, subtraction, multiplication, and division. The HP-35 and subsequent models have replaced the slide rule, used by generations of engineers and scientists. The HP-35 performed all the functions of the slide rule to ten-digit precision over a full two-hundred-decade range.''


Hitachi is one of pioneers in electron microscopes, which it first started research and development in 1940, and has developed many electron microscopes. Its microscopes, beginning from the first made-in-Japan commercial electron microscope in 1942 [1a], have been highly evaluated from early on, for example the grand prize at the Brussels International Exposition in 1958.
Developed by Hewlett-Packard Company in Palo Alto, California at 1501 Pagemill Road and introduced in 1972, the HP-35 was the first full-function, shirt-pocket-sized, scientific calculator. This invention revolutionized the profession by allowing the engineer to make almost instantaneous, extremely accurate scientific calculations, at his home, office or in the field. Three to five hours of continuous use could be expected from a fully charged battery pack.
<br>
[[Image:HP 35 Milestone invitation001.jpg|thumb|left|250px]]
<br>


In the mid-1960's, Dr. A. V. Crewe (The University of Chicago) developed a field emission (FE) electron source and a high-resolution FE scanning transmission electron microscope (FE-STEM) [2a, 2b], and reported visibility of single atoms by using the FE-STEM [2c].&nbsp; Hitachi collaborated with Dr. Crewe in the development of a practical FE electron microscope. After many years of fundamental research and development of FE technology [3a, 3b], Hitachi succeeded to develop the world’s first commercial high-resolution FE-SEM (field emission scanning electron microscope) in 1972 [4a], [4b], [Photo 1].&nbsp; The FE-SEM brought about an innovative improvement in image resolution, from 15 nm to 3 nm. Its first application was to biology, which resulted in the first high-resolution observation of T2-bacteriophages [Photo 2a]. The later application of microprocessor control technology [5a] and an enhanced in-lens electron optics design [5b] enabled ultra-high-resolution imaging of sub nanometers, which led to more detailed images of T2-bacteriophages [6], [Photo 2b], and the first observation of the AIDS virus. Subsequent advances in technology resulted in current FE-SEMs having greatly improved resolution, i.e., 0.4 nm in the secondary electron image.<br>The FE electron source was also applied to a transmission electron microscope (TEM) and a scanning transmission electron microscope (STEM). In physics, the application of an FE electron source with high interference characteristics to an FE-TEM developed for electron beam holography resulted in greatly improved coherency, i.e., from 300 to as many as 3000 lines of Fresnel fringes [7a]. The FE-TEM electron beam holography experimentally proved the Aharonov-Bohm effect in 1982, which confirmed the existence of gauge field and put an end to the vector-potential controversy. [7b, 7c,7d], [Photo 3].&nbsp; In the semiconductor industry,&nbsp;a critical-dimension SEM (CD-SEM), i.e., an FE-SEM dedicated to semiconductor-device micro-pattern in-line measurement, was commercialized in 1984[8a]. The CD-SEM is suitable for measuring non-conductive semiconductor devices without charge-up. Application of the Schottky electron source, an FE electron source proposed by Dr. Swanson in the 1980's, enabled long-term, stable and reliable CD-SEM operation, which is required for semiconductor production lines. CD-SEMs have been contributing to “scaling” as an indispensable metrology tool for device fabrication [8b], [8c].&nbsp; Development of FE electron source technology enabled ultra-high-resolution imaging with stability and reliability. FE electron microscopes, i.e., FE-SEMs, FE-TEMs, FE-STEMs, and CD-SEMs, are now widely used for advanced research and development in many fields of science, technology, and industry, including physics, biotechnology, medical science, materials, and semiconductors.<br>
The HP-35 was the innovative culmination of mechanical design, state-of-the-art technology, algorithm development and application; all unique at the time


The FE electrons are obtained by applying a high voltage (several thousand volts) to the tip of a metal needle (FE tip) with a radius of less than 100 nm. Application of a high electric field to the tip extracts electrons from the top of the tip due to the tunnel effect, whereas heating of the tungsten filament in a conventional thermionic emission source extracts thermionic electrons.&nbsp; Because of the high electric field, the FE electron current density (10<sup>4</sup>–10<sup>6</sup> A/cm2) is three orders of magnitude larger than that of thermionic electrons (1–10 A/cm<sup>2</sup>). An FE electron source is ideally a point source, and the diameter of the virtual source ranges from 5 to 10 nm, which is 1/1000 the source size of thermionic emission (1–10&nbsp;micron meters). The energy spread of FE electrons is 0.2–0.3 eV, which is much narrower than that of thermionic emission (2 eV). As a result, an FE electron source has 1000× the brightness, 1/1000 the source size, and 1/10 the energy spread of a conventional thermionic emission source. These features of the FE electron source result in much brighter and higher resolution images and high interference characteristics when applied to SEMs, TEMs, STEMs, and CD-SEMs. However, the instability of the FE emission current was an essential difficulty in the development of a practical FE electron microscope. After many years of fundamental research and development of FE electron source stability technology, Hitachi finally achieved a commercial FE-SEM featuring a stable and reliable FE electron source.<br>For FE emission current stability, a steady-state ultra-high vacuum of 10<sup>−8</sup> Pa was necessary since residual gas molecules cause the FE emission current to fluctuate. This is a much higher vacuum than that of a conventional thermionic emission electron source (order of magnitude of 10<sup>−4</sup> Pa). Moreover, maintaining an ultra high vacuum under electron beam emission conditions is quite a challenge because the electron beam stimulates outgassing from the anode, which degrades the vacuum.<br>Hitachi succeeded in establishing an ultra-high vacuum technology for the FE electron source. Patented "innerbake” technology [9], i.e., heating and degassing of a heater built into the anode, was the breakthrough. A “flashing" technique, i.e., short-duration heating of the cathode to remove the gas molecules, produced a stable, clean state of the cathode surface. Low outgas materials and surface treatment technology were also integrated and used to reduce the effect of the residual gas molecules. A canceling technique against beam fluctuation enabled high resolution imaging. [10]. As a result, the FE emission current was fundamentally stabilized, enabling a stable and reliable FE electron source, which realized the development of practical high-resolution electron microscopes.<br>&lt;/p&gt;
After the development of the HP-9100 desktop scientific calculator in the mid 1960s, Bill Hewlett, president of Hewlett-Packard envisioned the idea that HP could develop the same capability that would fit in his shirt pocket. Every few months he would walk into the corporate labs and ask how the team was doing? He stressed how important it was to get the calculating power of the desktop in his fingers.  


== References and Further Reading  ==
Although semiconductor density was increasing yearly, bipolar technology was never going to be suitable, too power hungry and not small enough. Metal Oxide Semiconductor (MOS) promised high density and low power but was still in its infancy. However this didn’t stop Bill Hewlett from getting the Industrial Design group of HP Labs to mock up some ideas of shape, key layout, etc. The solid state laboratory was also working on LED displays with molded encapsulated lenses for magnification driven by low power bipolar driver circuits.


[1] T. Komoda,, "Electron Microscopes and Microscopy in Japan, 4.5A Electron Microscope Development at Hitachi in the 1940s", Advances in Imaging and Electron Physics, Vol.96, p.653-657, (1996) [[Image:1 Komoda (1996).pdf|Image:1_Komoda_(1996).pdf]]<br>[2a] A. V. Crewe, D. N. Eggenberger, J. Wall and L. M. Welter, "Electron Gun Using a Field Emission Source", The Review of Scientific. Instruments, Vol.39, No.4, p.576-583 (1968) [[Image:2a Crewe(1968).pdf|Image:2a_Crewe(1968).pdf]]<br>[2b] A.V. Crewe, J. Wall and L. M. Welter, "A High-Resolution Scanning Transmission Electron Microscope", J. Appl. Phys. Vol.39, No.13, p.5861-5868 (1968) [[Image:2b Crewe(1968).pdf|Image:2b_Crewe(1968).pdf]]<br>[2c] A. V. Crewe, J. Wall and J. Langmore, “Visibility of Single Atoms”, Science, Vol.168, p.1338-1340 (1970) [[Image:2c Crewe(1970).pdf|Image:2c_Crewe(1970).pdf]]<br>[3a] T. Komoda and S. Saito, "Experimental Resolution Limit in the Secondary Electron Mode for a Field Emission Source Scanning Electron Microscope”, Scanning Electron Microscopy, Proc. 5th. Annual Scanning Electron Microscope Symposium, p.129-136 (1972) [[Image:3a Komoda(1972).pdf|Image:3a_Komoda(1972).pdf]]<br>[3b] T. Komoda, T. Tonomura, A. Ohkura and Y. Minamikawa, "A Scanning Transmission Electron Microscope Using a Field Emission Electron Gun”, Sixth International Conference on X-Ray Optics and Microanalysis, p.483-488 (1972) [[Image:3b Komoda(1972).pdf|Image:3b_Komoda(1972).pdf]]<br>[4a] "High-resolution Scanning Electron Microscope: Model HFS-2", Hitachi Review, Vol.21, No.6 (1972) [[Image:4a HitachiReview(1972).pdf|Image:4a_HitachiReview(1972).pdf]]<br>[4b] S. Katagiri, T. Komoda, K. Shiraishi and S. Saito, “Development of Field Emission Type High Resolution Scanning Electron Microscope (HFS-2)”, The Okochi Memorial Prize, Twenty-Second Technology Prize, p.28-32 (1976) [[Image:4b Katagiri OkochiPrize(1976).pdf|Image:4b_Katagiri_OkochiPrize(1976).pdf]]<br>[5a] S. Saito, Y. Nakaizumi, T. Nagatani and H. Todokoro, “Microprocessor Control of a Field Emission Scanning Electron Microscope (Model S-800)”, EMSA, Phoenix Arizona (1983) [[Image:5a Saito(1983).pdf|Image:5a_Saito(1983).pdf]]<br>[5b] T. Nagatani, S. Saito, M. Sato and M. Yamada, “Development of an Ultra High Resolution Scanning Electron Microscope by means of a Field Emission Source and In-Lens System”, Scanning Microscopy, Vol.1, No.3, p901-909 (1987) [[Image:5b Nagatani(1987).pdf|Image:5b_Nagatani(1987).pdf]]<br>[6] K. Tanaka, A. Mitsushima, Y. Kashima and H. Osatake, "A New High Resolution Scanning Electron Microscope and its Application to Biological Materials", Proc. XIth Int. Cong. on Electron Microscopy, Kyoto, p.2097-2100 (1986) [[Image:6 Tanaka(1986).pdf|Image:6_Tanaka(1986).pdf]]<br>[7a] A. Tonomura, T. Matsuda, J. Endo, H. Todokoro and T. Komoda, "Development of a Field Emission Electron Microscope", J. Electron Microsc., Vol.28, No.1, p.1-11 (1979) [[Image:7a Tonomura(1979).pdf|Image:7a_Tonomura(1979).pdf]]<br>[7b] A. Tonomura, T. Matsuda, R. Suzuki, A. Fukuhara, N. Osakabe, H. Umezaki, J. Endo, K. Shinagawa, Y. Sugita, and H. Fujiwara, "Observation of Aharonov-Bohm Effect by Electron Holography", Physical Review Letters, Vol.48, No.21, p.1443-1446 (1982) [[Image:7b Tonomura(1982).pdf|Image:7b_Tonomura(1982).pdf]]<br>[7c] A. Tonomura, "Applications of Electron Holography Using a Field Emission Electron Microscope", J. Electron Microsc., Vo.33, No.2, p.101-115 (1984) [[Image:7c Tonomura(1984).pdf|Image:7c_Tonomura(1984).pdf]]<br>[7d] A. Tonomura, N. Osakabe, T. Matsuda, T. Kawasaki, J. Endo, S. Yano and H. Yamada, "Evidence for Aharonov-Bohm Effect with Magnetic Field Completely Shielded from Electron Wave", Physical Review Letters, Vol.56, No.8, p.792-795 (1986) [[Image:7d Tonomura(1986).pdf|Image:7d_Tonomura(1986).pdf]]<br>[8a] T. Ohtaka, S. Saito, T. Furuya and O. Yamada, "Hitachi S-6000 Field Emission CD-Measurement SEM", SPIE Vol.565, Micron and Submicron Integrated Circuit Metrology, p.205-208 (1985)&nbsp; [[Image:8a Ohtaka(1985).pdf|Image:8a_Ohtaka(1985).pdf]]<br>[8b] Hitachi Ltd, Hitachi High-Technologies Corporation and Hitachi High-Tech Fielding Corporation, “Development and Commercialization of Critical Dimension Scanning Electron Microscope for Measurement of Ultra-fine Semiconductor Patterns”, The Okochi Memorial Production Prize (2007) [[Image:8b OkochiPrize(2007).pdf|Image:8b_OkochiPrize(2007).pdf]]<br>[8c] H. Obayashi, IEEE Ernst Weber Engineering Leadership Recognition (2010), <br>http://www.ieee.org/about/awards/bios/ernst_weber_recipients.html<br>[9] H. Todokoro and Y. Sakitani, " Field Emission Electron Gun with Anode Heater and Plural Exhausts", United States Patent 4295072 (Date of Patent&nbsp;: Oct 13, 1981) [[Image:9 Todokoro USP.pdf|Image:9_Todokoro_USP.pdf]]<br>[10] S. Saito, "Scanning type Electron Microscope",&nbsp;United States Patent 4588891 (Date of Patent&nbsp;: May 13, 1986)&nbsp; [[Image:10 Saito USP.pdf|Image:10_Saito_USP.pdf]]<br>
By 1970 a PMOS architecture looked promising as a candidate for scientific algorithms; a binary coded decimal (BCD) adder and 13 digit plus sign (56 bit) long multiple words in a serial circulating shift register (race track) arrangement that was very efficient of both chip size and power. The microcode word length was 11 bits; during final development shortened to 10 by having only an inferred conditional branch, a ten percent reduction in circuitry was significant at the time. The fourteen digits would just be sufficient for ten digit accuracy with an overflow or carry digit and two guard digits while still retaining sign information throughout the algorithmic iterations. The result could be displayed as either a signed mantissa and two signed exponent digits or variable length fixed point. The product had an arithmetic and register chip, control and timing circuit and several ROMs. A clock rate of 200 KHz was sufficiently high to calculate a transcendental function within a second.  


== Letter from the site owner giving permission to place IEEE milestone plaque on the property  ==
The HP-35 was truly a product which you knew would be successful because the engineer at the next bench wanted it.


[[Image:IEEE-Milestone Letter HitachiHighTech.pdf|IEEE-Milestone_Letter_HitachiHighTech.pdf]]
The ubiquitous slide-rule was obsolete within a year; the HP-35 could do all the functions of the slide-rule to ten digit precision and determine the decimal point or power of 10 exponent through a full two hundred decade range.  


[[Image:IEEE-Milestone Letter HitachiCRL.pdf|IEEE-Milestone_Letter_HitachiCRL.pdf]]
Hewlett-Packard Co. (Palo Alto, Calif.) received the IEEE Corporate Innovation Recognition honor in June 1989 for "the creation, development and introduction of the first full-function, shirt-pocket-sized, scientific calculator"- the HP-35.  


== Proposal and Nomination  ==
Forbes ASAP magazine called the HP-35 one of the twenty products that changed the modern world. The HP-35 and its descendants would sell more than 20 million units for Hewlett-Packard, making them the most popular products in the company’s history.


[[Milestone-Proposal:First Practical Field Emission Electron Microscope, 1972-1984]]
From the computer history museum: in 1972 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. The HP-35 distinguished itself from its competitors by its ability to perform a broad variety of logarithmic and trigonometric functions, to store more intermediate solutions for later use, and to accept and display entries in a form similar to standard scientific notation.


[[Milestone-Proposal:First Practical Field Emission Electron Microscope, 1972-1984]]  
Excerpt from the original manual; "The objective in developing the HP-35 was to provide a high precision portable electronic slide rule; something only fictional heroes like [[Technology in the James Bond Universe|James Bond]], Walter Mitty or Dick Tracy are supposed to own.
 
The HP-35 has far more computational power than previous pocket calculators. Its ten digit accuracy exceeds the precision to which most of the physical constants of the universe are known. It will handle numbers as small as 10^-99 and up to 10^99 and automatically places the decimal point. It is the first pocket calculator to offer transcendental functions like logarithms and sines and cosines. The operational stack and the reverse "Polish" (Lukasiewicz) notation used in the HP-35 are the most efficient way known to computer science for evaluating mathematical expressions.
 
The HP-35 was designed with the user, in mind. As much time was spent on the keyboard layout, on the choice of functions, and on the styling as was on the electronics."
 
At the time, many of the companies producing calculators could build adequate circuits and firmware, but didn't have the experience or facilities to make a well designed housing, keyboard, and display. Many of these brand-X machines were very failure-prone and quite crude in design.
 
By contrast, the packaging of the HP-35 was of major importance. Its size, looks, keyboard, and display were all carefully thought out. The keyboard is divided into groups with different sizes, color and placement of nomenclature. Even differing amounts of contrast were used to separate groups. (The most used groups had the greatest contrast level.) The keys were made in a double mold process with the legends going all the way through the keys so they could never wear off. The keyboard panel used an HP-developed spring contact which used bent beryllium copper strips. The key bottoms were designed to be easy on the copper while still providing the right feel which is essentially unchanged in current calculators.
 
The HP-35, like all the hand-held HPs that followed, was required to remain undamaged after falling three feet onto concrete on each of its corners. The case had sculpted sides, such that the top caught the light and the bottom was in shadow making the calculator look thinner than it really was. All screws were hidden.
 
Length: 5.8" - Width: 3.2" - Height: 1.3" - Weight: 8.7oz
 
The milestone plaque is located in the lobby of building 3U at the Hewlett-Packard laboratories, 1501 Page Mill Rd, Palo Alto, California, adjacent to where the development occurred.
 
'''See also:''' [[First-Hand:Origins of Hewlett Packard 35 (HP-35)|Origins of Hewlett Packard 35 (HP-35)]]  


== Map ==
== Map ==


{{#display_map:35.711768, 139.470085~ ~ ~ ~ ~Central Research Laboratory, Hitachi|height=250|zoom=10|static=yes|center=35.711768, 139.470085}}
{{#display_map:37.4118, -122.1478~ ~ ~ ~ ~Hewlett-Packard, Palo Alto, CA|height=250|zoom=10|static=yes|center=37.4118, -122.1478}}
 
[[Category:Profession|Calculator]] [[Category:Engineering education|Calculator]] [[Category:Educational technology|Calculator]] [[Category:Calculators|Calculator]]


[[Category:Computing_and_electronics|{{PAGENAME}}]]
[[Category:Educational_technology|{{PAGENAME}}]]
[[Category:Lasers,_lighting_&_electrooptics|{{PAGENAME}}]]

Revision as of 19:07, 6 January 2015

Development of the HP-35, the First Handheld Scientific Calculator, 1972

The HP-35 was the first handheld calculator to perform transcendental functions (such as trigonometric, logarithmic and exponential functions). Most contemporary calculators could only perform the four basic operations – addition, subtraction, multiplication, and division. The HP-35 and subsequent models have replaced the slide rule, used by generations of engineers and scientists. The HP-35 performed all the functions of the slide rule to ten-digit precision over a full two-hundred-decade range.

Developed by Hewlett-Packard Company in Palo Alto, California at 1501 Pagemill Road and introduced in 1972, the HP-35 was the first full-function, shirt-pocket-sized, scientific calculator. This invention revolutionized the profession by allowing the engineer to make almost instantaneous, extremely accurate scientific calculations, at his home, office or in the field. Three to five hours of continuous use could be expected from a fully charged battery pack.

HP 35 Milestone invitation001.jpg


The HP-35 was the innovative culmination of mechanical design, state-of-the-art technology, algorithm development and application; all unique at the time

After the development of the HP-9100 desktop scientific calculator in the mid 1960s, Bill Hewlett, president of Hewlett-Packard envisioned the idea that HP could develop the same capability that would fit in his shirt pocket. Every few months he would walk into the corporate labs and ask how the team was doing? He stressed how important it was to get the calculating power of the desktop in his fingers.

Although semiconductor density was increasing yearly, bipolar technology was never going to be suitable, too power hungry and not small enough. Metal Oxide Semiconductor (MOS) promised high density and low power but was still in its infancy. However this didn’t stop Bill Hewlett from getting the Industrial Design group of HP Labs to mock up some ideas of shape, key layout, etc. The solid state laboratory was also working on LED displays with molded encapsulated lenses for magnification driven by low power bipolar driver circuits.

By 1970 a PMOS architecture looked promising as a candidate for scientific algorithms; a binary coded decimal (BCD) adder and 13 digit plus sign (56 bit) long multiple words in a serial circulating shift register (race track) arrangement that was very efficient of both chip size and power. The microcode word length was 11 bits; during final development shortened to 10 by having only an inferred conditional branch, a ten percent reduction in circuitry was significant at the time. The fourteen digits would just be sufficient for ten digit accuracy with an overflow or carry digit and two guard digits while still retaining sign information throughout the algorithmic iterations. The result could be displayed as either a signed mantissa and two signed exponent digits or variable length fixed point. The product had an arithmetic and register chip, control and timing circuit and several ROMs. A clock rate of 200 KHz was sufficiently high to calculate a transcendental function within a second.

The HP-35 was truly a product which you knew would be successful because the engineer at the next bench wanted it.

The ubiquitous slide-rule was obsolete within a year; the HP-35 could do all the functions of the slide-rule to ten digit precision and determine the decimal point or power of 10 exponent through a full two hundred decade range.

Hewlett-Packard Co. (Palo Alto, Calif.) received the IEEE Corporate Innovation Recognition honor in June 1989 for "the creation, development and introduction of the first full-function, shirt-pocket-sized, scientific calculator"- the HP-35.

Forbes ASAP magazine called the HP-35 one of the twenty products that changed the modern world. The HP-35 and its descendants would sell more than 20 million units for Hewlett-Packard, making them the most popular products in the company’s history.

From the computer history museum: in 1972 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. The HP-35 distinguished itself from its competitors by its ability to perform a broad variety of logarithmic and trigonometric functions, to store more intermediate solutions for later use, and to accept and display entries in a form similar to standard scientific notation.

Excerpt from the original manual; "The objective in developing the HP-35 was to provide a high precision portable electronic slide rule; something only fictional heroes like James Bond, Walter Mitty or Dick Tracy are supposed to own.

The HP-35 has far more computational power than previous pocket calculators. Its ten digit accuracy exceeds the precision to which most of the physical constants of the universe are known. It will handle numbers as small as 10^-99 and up to 10^99 and automatically places the decimal point. It is the first pocket calculator to offer transcendental functions like logarithms and sines and cosines. The operational stack and the reverse "Polish" (Lukasiewicz) notation used in the HP-35 are the most efficient way known to computer science for evaluating mathematical expressions.

The HP-35 was designed with the user, in mind. As much time was spent on the keyboard layout, on the choice of functions, and on the styling as was on the electronics."

At the time, many of the companies producing calculators could build adequate circuits and firmware, but didn't have the experience or facilities to make a well designed housing, keyboard, and display. Many of these brand-X machines were very failure-prone and quite crude in design.

By contrast, the packaging of the HP-35 was of major importance. Its size, looks, keyboard, and display were all carefully thought out. The keyboard is divided into groups with different sizes, color and placement of nomenclature. Even differing amounts of contrast were used to separate groups. (The most used groups had the greatest contrast level.) The keys were made in a double mold process with the legends going all the way through the keys so they could never wear off. The keyboard panel used an HP-developed spring contact which used bent beryllium copper strips. The key bottoms were designed to be easy on the copper while still providing the right feel which is essentially unchanged in current calculators.

The HP-35, like all the hand-held HPs that followed, was required to remain undamaged after falling three feet onto concrete on each of its corners. The case had sculpted sides, such that the top caught the light and the bottom was in shadow making the calculator look thinner than it really was. All screws were hidden.

Length: 5.8" - Width: 3.2" - Height: 1.3" - Weight: 8.7oz

The milestone plaque is located in the lobby of building 3U at the Hewlett-Packard laboratories, 1501 Page Mill Rd, Palo Alto, California, adjacent to where the development occurred.

See also: Origins of Hewlett Packard 35 (HP-35)

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