The HP-41C: A Legend Is Born

Because I tend to reminisce in my Field Notes installments from time to time, it seems fitting to include the computing workhorse of my generation, the Hewlett-Packard 41C series. It carried me through the most developmental stage of my career and will remain my favorite calculator of all time. 

HP 41C

The HP 41C, image credit: the Museum of HP Calculators

The first HP-41C was introduced in 1979 as the first HP calculator to offer alphanumeric capabilities, both on the keyboard and display, providing greatly enhanced programming functionality. However, unlike many of my peers, I never actually wrote any programs for my 41-C series calculators because the expandable modules offered everything that I needed. Oh, and I was an epic failure at programming of any kind. 

In addition to the alphanumeric capability, the HP-41C (first version in the series) came with 63 “registers” of memory, which could be reassigned between storage memory and program memory. The four ports on the top allowed users to plug in additional RAM modules, offering additional register or program space. It was revolutionary! 

I was first introduced to the legend in 1983, when my employer at the time presented me with a brand new 41C as my goingaway gift after having been his only employee for the previous two years. I was relocating for my wife to attend college, then my plan was to attend engineering school upon her completion. As an appreciation for my service and encouragement to pursue engineering school, my boss invested about $300 in me, which was a lot of money back then—certainly, more than I could afford. At the time, I had no idea how much that investment would pay off. Thank you, Mr. Schneider. 

Upon relocation in August of 1983, I quickly landed a job at an engineering firm working on the field crew and performing office duties as needed. My party chief also had a 41, but his was the newly released CX model, which had advanced memory capabilities and a time module, and a few additional features. Still, my C model was useful in the field and I soon bought a leather pouch for it.  

But, I needed more functionality in the form of modules, so I bit the bullet (about $400 if my memory is correct) and invested in the CX with the survey module. With each module came an overlay board to show the keyboard functions when running that module. Brilliant! 

Besides my growing field role at work, I was starting to study for the Land Surveyor-in-Training (LSIT) examination and enrolled in evening survey courses at the local community college. I was quickly becoming familiar with my new and powerful 41CX and loving it. Horizontal and vertical curves? No problem. Traversing and inversing, including areas calculations? A breeze. Bearing-bearing intersections? Simple.  

Writing down coordinates (or storing them) and watching the “goose” fly across the screen was a small price to pay for having a computer in my hands. I was using it so much in the field that I bought customized Ziplocktype baggies to seal the dust out of it. I went through a bunch of those in the day. 

Over the next few years, I successfully passed the LSIT examination and the California Professional Land Surveyor examination and enrolled in engineering classes full-time. I had purchased the statistics module, at least, and rarely went anywhere without my 41CX on my hip or in my backpack. Although few of my classmates in the engineering program had 41C series calculators, none of them had logged the hours on them that the “old man” in the classes had. 


I specifically recall participating in a study group for a physics course in the library one afternoon. We were studying multiple forces on an object (known as a free-body diagram)all pulling or pushing with different magnitudes of forces in different directions. Think of a pack of large and small dogs pulling on an object in different directions all at once. 

We were taught two methods of solving what the result would be on that object: which direction would it move and how

fast? The forces were typically given something like this: Force 1) 10 Newtons up by 6 Newtons to the right, and so on.  

Resultant vector 1

One method was to use right triangle trigonometry to calculate the hypotenuse magnitude and direction for each force to get the “resulting vector from that force. You then linked each resulting vector for all the forces given in the problem head-to-tail in any order. Then you used trig to solve for the final direction and magnitude.  The other method was to plot the vectors at scale using a protractor, then measure from the head of the last vector to the tail of the first vector. This required careful “drafting.  

As my study partners started breaking down each vector, it suddenly dawned on me that this was simply an open-ended traverse with an inverse from the beginning to the end of the last leg. I pulled out my 41CX, fired up the survey module, assumed some coordinates, and went to work. I started writing down coordinates along the way. My study partners had no clue what I was doing, other than apparently wasting time. I got to the end of the traverse, then inversed back to the origin and blurted out the resulting vector “answer.” We had the solutions book, which verified that I was correct. Their jaws dropped. Freaking magic!  

Resultant vector 2

They asked how I did that by writing down gibberish, and I said, “It’s simply an openended traverse and an inverse back to the beginning.” What? The “old man” knew great things, in their minds, but they had no idea what I was talking about and were doomed to slog their way through one of the other methods. I was elevated to a new standing that day. 


Fastforward a few years. A colleague and former mentor (the same party chief who showed me the CX) who ran the survey program at a small engineering firm had purchased a new HP-48 as a data collector. He stopped by our firm to excitedly show off his new “toy.” Another PLS from our firm was there too. He explained how he was going to use it as a data collector; then we asked to put our hands on it. The display was foreign compared to the beloved 41, but it was just another HP calculator with reverse polish notation, right? For the next 20 minutes, the three of us tried, and failed, to multiply any number times Pi.  

I believe they did deploy the 48 as a data collector, but I realized that afternoon that I had attained my calculator user plateau with the mastery of the 41CX and that no successor could ever compare. That remains true to this day. I now have several 41C series calculators in my “fleet” along with many accessories, even though I haven’t needed to use one for surveying calculations in many years. But I have no doubt that I could. The LTCME entry option for solving horizontal curves is still etched in my memory. As is the day I performed magic for my classmates. 

Field Notes

This article appeared in xyHt‘s e-newsletter, Field Notes. We email it once a month, and it covers a variety of land surveying topics in a conversational tone. You’re welcome to subscribe to the e-newsletter here. (You’ll also receive the twice-monthly Pangaea newsletter with your subscription.)


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The HP-41C: A Legend Is Born” Comments

  1. Great article.

    pretty much mirrors my experience with the 41C and CX.
    I still have four of them (one seems to be dead at the moment.

    Will pick one of those up before I reach for a 48.


  2. I too bought and used my 41CV in both private and public Civil Engineering. I bought mine in the early years (early 80’s) and still use it today. I had many of the program software chips and also became proficient in writing programs for it. I love it! I especially like the RPN as anyone trying to use it will fail, asking where the equal key ‘=’ is at. It is with me at this time to double check any questions I may have with the programs on the computer I run even excel spread sheet.
    It’s a good old friend that I will not give up.

    It was once advertised as having more program power than the computer that went to the Moon!

  3. Loved your article. I still use a 41CV with a Sup-R-Rom module that I bought back in the 80’s. I find that the simplicity of the programs and its use help me to provide my survey expertise to a local conservation trust in monitoring the property lines of their 70 odd parcels of land here on Cape Cod.


  4. I fully agree, the best for me has always been the HP 41 family of calculators. My first of two 41’s dates back decades now, and even though I have added the 48’s (as data collectors, then upon retirement each desk in my office would have one for a quick grab to check something) and then even the HP 50, personally the 41CV & CX are still my favorites, and i still use them day to day to check closures.

  5. You are right – nothing like it has been made since. Thanks to HP it’s available for your smart phone – I use it constantly.
    I read, on the original space shuttle mission, five HP-45’s in environmental cases were aboard to serve as backup computers for flight control.
    Compact, powerful, and capable.
    Try finding a calculator with RPN today!

  6. It’s so nice to know there are other people who appreciate tools like the HP-41 and write about it!
    I had an HP-41CV in the 1980s (alas, it died and I haven’t found anyone to fix it). I used it mostly for solving mechanical engineering problems, but what I remember best is how it hacked a computer game. There was a submarine game for the Commodore 64. If you were submerged you could use the Torpedo Data Computer to get firing solutions to hit an enemy ship while both you and it were moving. But on the surface, with the 5-inch deck gun, you had only your own sense of “Kentucky windage” to figure out where to point the gun and when to fire – not conducive to a long life if you were facing a ferocious Kaibokan destroyer. At the cost of many of my own “lives” I figured out the ballistics of the 5-incher, and wrote a program for the 41CV that would give me a firing solution that was faster and better than that of my cybernetic adversary. Me and my HP quickly became the undefeatable submarine in the Commodore navy!

  7. When working for GE Ultrasound, I used the HP-41C and created an “OB/GYN” calculator with custom keyboard and ROM. Basically before machines has the feature, The pocket calculator would give you gestational age from one or more measurement inputs. Typical back then were: BiParietal Diameter, Femur length, and abdominal circumference. Today ultrasound machines have this and much more per programmed.

  8. A 41CX sits on my desk, and gets used a lot. After 47 years, I figure when it quits, I retire

    But then there is the spare in the drawer, so retirement looks way off.

    I bought a 21 when they first came out and it would hold 49 steps of programmable memory, but would lose it if you turned it off. I wrote a closure program for it that used exactly 49 steps, and my old party chief just loved me to run closures without looking up trig functions. Guess that shows my age!

  9. Oh Man! I loved the HP-41!
    Wrote many programs for it. One allowed ray out of points on a multi leg curve and tangent Alinement by Station/Offset. Also, Calc the inverse of that. It revolutionized our Construction Staking. Slope Stakes were a breeze.
    Wrote a CoGo program that stored points onboard. A feature sadly lacking in the Module program. (Why??)
    Someone made available the program that was used aboard the early Space Shuttle for tracking ground station visibility. Not much use for us but just cool. Sun Shots for Traverse Azimuth Checks were done all the time.
    After retiring I got an HP Prime calculator and wrote a powerful CoGo program but was used for fun and occasionally helping a friend or neighbor with a surveying issue.

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