The Wands of Power

 

Pickett N3-ES Log-Log Decitrig, eye-saver yellow on aluminum

HP-16C Programmers Calculator

A Pickett N3-ES Log-Log Decitrig, eye-saver yellow on aluminum, in the drawer next to my HP-16C. Both still working, both still on the desk, both representing the same function across changes of substrate. And — almost as important — both representing the end of something. My engineering class at the University of Maryland was the last one required to learn the slide rule, the T-square, and the drafting triangle. We were the last cohort to be issued the engineer's wand of power.

By Stephen "Pseudo Publius"  |  7 May 2026

BLUF — 

 In the drawer next to my desk in San Diego sit two instruments. The first is a Pickett N3-ES Log-Log Decitrig slide rule — eye-saver yellow paint photo-printed on a precision-machined aluminum body, 32 scales, 10-inch scale length, manufactured in California by Pickett Industries somewhere between 1960 and 1975. It is the engineering student's tool from the period when American engineering education was at the peak of its mechanical-instrument tradition. The Pickett N600-ES, the 6-inch pocket version of the same Log-Log Speed Rule family, was the slide rule Buzz Aldrin carried to the Moon aboard Apollo 11; it flew on the first five Apollo missions because Pickett's all-aluminum construction was lighter than K&E's mahogany and could not warp in the temperature and humidity extremes of spaceflight. The second instrument is a Hewlett-Packard 16C "Computer Scientist" pocket calculator, 1982, the breakthrough programmer's tool described in the previous installment of this series. The two instruments share a drawer because they served the same function in succession — engineer's personal calculating instrument on the desk — across a transition that happened, in American engineering education, between roughly 1972 and 1976. My undergraduate engineering class at the University of Maryland was the last class required to learn the slide rule, the T-square, and the drafting triangle as instruments of the profession. We were also among the first to encounter the HP-35 pocket calculator that was, simultaneously, making the slide rule obsolete. The two instruments in my drawer are the artifacts of that transition.^1,2,3

The Pickett company, briefly

The Pickett & Eckel Company was founded in Chicago in 1943 by Ross C. Pickett. From the beginning Pickett's identity was different from Keuffel & Esser's — K&E was the established Eastern firm, eighty years old by then, with an institutional culture rooted in mahogany craftsmanship and German-American precision drafting. Pickett was a postwar California-oriented startup (the firm moved manufacturing to Alhambra, California, in the early 1950s and to Santa Barbara in 1964) whose entire product strategy was built around a single materials decision: do not use wood. Every Pickett rule was metal — initially magnesium alloy, then aluminum from the early 1950s onward.¹

The metal-versus-mahogany distinction looks small in retrospect but was decisive at the time. K&E's mahogany rules were beautiful objects but had real engineering limitations: the wood expanded and contracted with humidity, the celluloid scales could lift in tropical conditions, the rules required careful storage and could warp if left in the sun. Pickett's aluminum rules had none of these problems. They could sit in a hot car. They could be dropped on concrete. They could be carried in a damaged leather case for thirty years and still read accurately. The aluminum was also significantly lighter than mahogany of equivalent stiffness, which mattered for engineers who carried rules in shirt-pocket cases all day.

Pickett's second innovation was visual. By the mid-1950s the company had introduced "Eye Saver" yellow — a specific paint formulation, photo-printed on the aluminum surface, calibrated to reduce eye strain under fluorescent classroom and office lighting that was becoming standard in postwar American engineering buildings. The yellow background with black scale markings produced higher contrast under fluorescent illumination than the white background K&E used, and the photo-printing process produced sharper edges than K&E's engraved-and-inked celluloid. Pickett's "ES" suffix on its model numbers — N600-ES, N3-ES, N902-ES — meant Eye Saver. The "T" suffix meant traditional white. By the early 1960s, Eye Saver yellow had become the dominant Pickett finish and a visible signature of the brand.¹

The N3-ES specifically

The Pickett N3-ES was Pickett's flagship engineering rule, produced from 1960 to 1975. It came in two sizes: the standard N3-ES (12 inches long with 10-inch scales) and the pocket N3P-ES (7.5 inches long with 5-inch scales). The N3-ES carried 32 scales — more than the K&E 4081's 21 and more than the K&E Deci-Lon's 26, putting it among the most heavily-scaled slide rules ever produced. The scale set included:²

• The basic C, D, CI, DI for multiplication, division, and reciprocals
• A, B (squared) and K (cubed) for powers and roots
• CF, DF, CIF folded scales for chain calculations across decades
• S, ST, T1, T2 trigonometric scales calibrated in decimal degrees (the "Decitrig" feature)
• L, Ln common-logarithm and natural-logarithm scales
• LL0, LL1, LL2, LL3 log-log scales for arbitrary exponents — the "Log-Log" capability
• √#1, √#2, ³√#1, ³√#2, ³√#3 dedicated square-root and cube-root scales for higher precision than reading from A and K

The 32-scale design was, frankly, more capability than most students needed. But it was the rule that handled every undergraduate engineering problem set in every discipline — circuits, statics and dynamics, thermodynamics, fluid mechanics, structural analysis, control systems — without requiring you to switch instruments. For a working engineer, the N3-ES was a single tool that did the entire pre-calculator job. Skilled users could read three significant figures directly off the scales and estimate a fourth by interpolation, which was sufficient for nearly all engineering calculations of that era.

To the Moon and back

The Pickett rule's most famous moment came on 20 July 1969, when astronaut Edwin "Buzz" Aldrin descended from the lunar module Eagle onto the surface of the Moon, with a Pickett N600-ES (the 6-inch pocket version of the same Log-Log Speed Rule family as my N3-ES) clipped to the leg pocket of his EVA suit. NASA had selected the Pickett N600-ES specifically for the Apollo program because the aluminum construction met two requirements that the mahogany K&E rules could not: it was lighter, and it could not warp under the thermal cycling and pressure changes of spaceflight. The N600-ES flew on the first five Apollo missions — Apollos 7, 8, 9, 10, and 11. Aldrin's particular rule was sold at Heritage Auctions on 20 September 2007 for $77,675.³

The Apollo 13 emergency in April 1970 cemented the slide rule's place in the American engineering imagination. When the Apollo 13 oxygen-tank explosion forced Mission Control to recalculate the lunar-module ascent burn duration that would bring the spacecraft home — a calculation that had not been planned and that the onboard computers were not configured to perform on short notice — the verification calculations on the ground at Houston were done on slide rules at the Mission Control consoles. Pickett rules and K&E rules were both present, with the consoles dominated by Pickett models because of their durability under heavy daily use. The result was sufficiently accurate. The crew came home on 17 April 1970.⁴

So the rule that sat in my engineering student's belt-loop case at the University of Maryland in the early 1970s was, model-line for model-line, the same rule that Mission Control had used to bring Apollo 13 home and that Aldrin had carried to the lunar surface eighteen months before that. This is, I think, the right thing for an undergraduate engineering student to know about the instrument in his hand. It establishes both the tool's seriousness and the lineage the student is being trained to enter.

The wand of power

Engineering students of my generation carried the Pickett (or K&E, or Post, or whichever rule the student had inherited or could afford) in a leather belt-loop case at all times during the school day. The case had an orange-leather front flap with the manufacturer's logo embossed in gold, a snap closure, and a metal belt clip that allowed the rule to ride at the right hip. Walking across the College Park campus from the engineering quadrangle to the dining hall, you could identify every engineering major at fifty feet by the rule on his belt. Students in liberal arts and the humanities did not carry rules. Pre-medical students did not carry rules. Business students did not carry rules. Engineers did. The rule was the visible badge of the field, the way the stethoscope identifies a doctor and the tool belt identifies a tradesman.

I called it the wand of power because that is what it was. With a Pickett N3-ES on your belt, you were not just a college student. You were the latest member of the lineage that ran through Apollo Mission Control, through the Manhattan Project (where K&E and Pickett rules sat next to the Marchants on the desks at Los Alamos and Aberdeen), through the 19th-century engineers who designed the Empire State Building and the Hoover Dam, through Brunel and Eiffel and Roebling and the entire 19th-century tradition of mechanical and civil engineering. The slide rule was the instrument that connected an undergraduate at Maryland in 1973 to that entire lineage. It was a real connection. The rule on my hip did the same arithmetic, on the same logarithmic principles invented by Napier in 1614 and implemented by Oughtred in 1622, that had been performed by every previous generation of working engineers for three and a half centuries.⁵

The wand was also a tool of the trade in the most literal sense. The engineering homework problem set required the slide rule the way a carpenter's job required a saw. You did not get through the problem set without the rule. You did not pass the engineering courses without the problem set. The integration of the instrument with the curriculum was total. Engineering Graphics — the required course in technical drawing — required the T-square (a graduated wood-and-metal straightedge anchored against the edge of the drafting table for horizontal lines), the 30-60-90 and 45-45-90 plastic triangles (for vertical and angled lines), the engineering compass and dividers (for arcs and circles), French curves (for irregular shapes), the lead holder with various hardness leads (2H for construction lines, F or HB for object lines, B for lettering), and the lettering guide. Every formal engineering drawing was made by hand on white drafting paper with these tools. There was no other way to do it.

The class that was the last

My engineering class at the University of Maryland was, I am fairly confident, the last class at that institution required to learn the slide rule and the manual drafting tools as instruments of the profession. The HP-35 had shipped in January 1972 at $395 — about three weeks of an engineering graduate's salary at the time. By 1973-1974 the HP-45 and the Texas Instruments SR-50 had brought the price down. By 1975 the cheap programmable HP-25 was within reach of most undergraduates. The university's calculation policy on examinations shifted from "slide rule only" to "slide rule or calculator, student's choice" to "calculator preferred" within roughly three years. By the time my class graduated, students one or two years behind us were arriving in engineering school having never owned a slide rule and not being required to acquire one.^5,6

The drafting transition took longer because the alternative was not a $395 calculator but a $50,000 Computervision or Intergraph CAD workstation that no undergraduate could access. The T-square and triangle requirement persisted at most engineering schools through the late 1970s, weakened in the early 1980s as PC-based AutoCAD made CAD accessible at the workgroup level, and disappeared from required curricula by the early 1990s. Today a graduating mechanical engineering student at the University of Maryland will have used SOLIDWORKS, AutoCAD, and probably Onshape; they will not have used a T-square. The T-square is in the same drawer as the slide rule and the HP-16C. There is also a leather case for the slide rule, with a belt clip, in the drawer.

The 1972-1976 transition, in dates

The compression of the slide rule's commercial life into a 48-month window between 1972 and 1976 is one of the cleaner technology-substitution events in 20th-century American engineering. Selected dates: January 1972: HP-35 ships at $395. 1973: HP-45 and TI SR-50; the price-and-feature tradeoff begins to favor calculators decisively. 1974: HP-65 (programmable) and major engineering schools begin allowing calculators on examinations. 1975: Pickett ceases slide rule production after 32 years. July 1976: K&E ships its last slide rule (a Deci-Lon) to the Smithsonian, ending 85 years of American slide rule manufacturing. 1977: TI Programmer brings hex/octal conversion to the pocket. 1978: HP-41C with plug-in modules. April 1982: HP-16C Computer Scientist — the breakthrough programmer's calculator I bought soon after it shipped and have used since. The slide rule had a 354-year run from Oughtred 1622 to its commercial extinction in 1976. The HP-16C, in 1982, took its place. The two instruments share a drawer because they belong, despite the substrate change, to the same engineering tradition.^1,6

What both instruments share

Open the drawer next to my desk. The Pickett N3-ES is in its leather case, the eye-saver yellow scales still bright through the cellophane window in the front flap, the aluminum still flat after sixty years, the cursor still tracking precisely. The HP-16C is in its black vinyl case, all keys responsive, the LCD still crisp on its original CMOS continuous memory, four battery changes in forty-three years. Both work. Both will, on current evidence, continue to work indefinitely.

What they share is not the technology — the technology could not be more different. The Pickett is mechanical, analog, three-significant-figure, requires the user to track the decimal point, and produces results by physically aligning marks on photo-printed logarithmic scales. The HP-16C is electronic, digital, ten-significant-figure (in floating-point mode) or arbitrary-word-length (in integer mode), tracks the decimal point automatically, and produces results by executing microcode on a CMOS processor. The Pickett is aluminum and yellow paint and plastic and leather. The HP-16C is plastic and silicon. The Pickett is silent. The HP-16C clicks.

What they share is the function. Both are an engineer's personal calculating instrument, sized to be on the desk or in the shirt pocket, designed to perform fast cross-checks of larger calculations being done elsewhere. The Pickett verified the work of hand-computed engineering tables, mainframe FORTRAN runs, and (in the late period) early electronic computer outputs. The HP-16C verified the work of AN/UYK-7 memory dumps, embedded-systems firmware listings, and tactical-software algorithm traces. The class of work — engineer's verification of a faster calculation, on a personal instrument, at the desk — is one continuous tradition. The Pickett is the last analog member of that tradition. The HP-16C is the early digital member. They sit together in the drawer because they belong to the same lineage.

Coda: durability

I want to close on the durability point because it is the one that, in the long view, will matter most.

The Pickett in my drawer is roughly sixty years old. It works. The HP-16C in my drawer is forty-three years old. It works. The Marchants the women at Aberdeen and Los Alamos used in the 1940s — many of them are still operational in museum and private collections, eighty years on. The rebuilt Bletchley Colossus at the National Museum of Computing runs eighty-two-year-old electronic logic at slower-than-original speed but with full functional integrity. The Pickett N600-ES that Buzz Aldrin carried to the Moon in 1969 sold at Heritage Auctions in 2007 for $77,675; it is now in a private collection. It still works.

The Memphis Colossus that opened this series has a designed operational lifetime of roughly five to seven years before its GPUs are retired and replaced. The orbital constellation that the deal contemplates has, by SpaceX's own filing, a five-year deorbit lifecycle — meaning each individual satellite is intended to burn up in the upper atmosphere within five years of the end of its useful life. The substrate of the most computationally significant infrastructure being built today is, by design, more disposable than any computational substrate that has ever existed.

This is not necessarily wrong. There are reasonable engineering and economic arguments for it. But it is a difference. A working engineer in 2080 — should there be such a person, doing recognizably similar work — will be able to open a museum drawer and use my Pickett N3-ES to perform a calculation. They will not be able to find a single working artifact from the orbital data center constellation, because every component of that constellation will, by design, have burned up over the South Pacific decades earlier. The most durable engineering of the late 20th century is sitting in my drawer in San Diego. The most ambitious engineering of the early 21st century is, by its own design specifications, the most ephemeral.

What this means for the long historical assessment of the present moment, I cannot say with confidence. But I notice that the engineering tradition that produced the Pickett N3-ES in 1960 and the HP-16C in 1982 was a tradition that took durability seriously as an engineering value — that designed for sixty-year service lives, that specified leather cases and aluminum bodies and CMOS continuous memory because the engineers building those instruments expected the engineers using them to keep using them for a working lifetime. The engineering tradition that is producing the Memphis Colossus and the orbital constellation in 2026 has, on its public statements, a different value structure. Speed of deployment, scale of capacity, throughput, and disposability are the dominant metrics. Service life, durability, and reparability are not. This may turn out to be the right trade-off for the moment. It is, however, the first computational substrate in human history that has been designed without any expectation of long-term physical persistence.

Whether the 2026 substrate proves more historically consequential than the 1965 substrate is for someone else, in the future, to judge. What I can say, sitting at my desk this evening, is that the two instruments in the drawer next to me will outlast every component of the deal that opened this series. The Pickett is older than my professional career. The HP-16C is forty-three. They both still work. The desk is the same desk it was when I bought them. The hand opening the drawer is the same hand that carried the Pickett in a leather case across the College Park campus in 1973, that calibrated the AN/UYK-7 in the late 1970s, that signed off on Lynx SAR/GMTI radar designs in the 2000s, and that types this sentence in 2026.

The engineering tradition that issued me the wand of power as an undergraduate did not last. My class was the last to receive it. But the wand still works. It is in the drawer. The HP-16C beside it still works too. The substrate of the work changes every generation. The work itself, and the desks and hands that perform it, do not. That is the answer to what this whole series has been about. The slide rule and the calculator in the drawer are the proof.

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Sources

1. "Pickett N3-ES & N3P-ES." Slide rule technical reference. https://sites.google.com/gpapps.galenaparkisd.com/myrules/all-purpose/pickett-n3-es-n3p-es  |  "Pickett N500-N600." https://sites.google.com/gpapps.galenaparkisd.com/myrules/all-purpose/pickett-n500-n600   Documents Pickett company history (founded 1943 in Chicago, moved to Alhambra 1950s, to Santa Barbara 1964), the magnesium-to-aluminum transition in the early 1950s, and the Eye Saver yellow innovation in the mid-1950s.
2. "Pickett N600-ES Log Log Duplex Slide Rule." Smithsonian National Museum of American History. https://americanhistory.si.edu/collections/object/nmah_694174   Documents the N600-ES specifically, including its Apollo provenance (carried on the first five Apollo flights). National Air and Space Museum inventory number A19840160000.
3. "Rules to the Moon." Following the Rules slide rule collection reference. https://followingtherules.info/rules-to-the-moon.html   Comprehensive documentation of the Pickett N600-ES on Apollo missions, including the September 2007 Heritage Auctions sale of Buzz Aldrin's Apollo 11 N600-ES for $77,675.
4. Mindell, D.A. Digital Apollo: Human and Machine in Spaceflight. MIT Press, 2008. Standard scholarly history of Apollo computing including the role of slide rules at Mission Control during Apollo 13.
5. Cajori, F. A History of the Logarithmic Slide Rule and Allied Instruments. Engineering News Publishing, 1909. Reprinted Astragal Press, 1994. Standard scholarly history of the slide rule from Napier (1614) and Oughtred (1622) through the modern duplex form.
6. "A K&E Plastic Slide Rule Timeline Study." Following the Rules Substack, January 2026. https://followingtherules.substack.com/p/a-k-and-e-plastic-slide-rule-timeline   Documents the K&E shutdown in July 1976 and the broader 1972-1976 American slide rule industry collapse following the HP-35 introduction. Pickett's parallel shutdown around 1975 is documented in Ref. 1.