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HP Calculators - RPN

Updated on April 2, 2013

Hewlett-Packard RPN Scientific Calculators

In the early 1970's, Personal Computers hadn't been invented and the slide rule was the standard way to make scientific and complex mathematical calculations. In 1972, a small company called Hewlett-Packard put an end to the slide rule era with the introduction of the HP-35, the world's first scientific calculator. The HP-35 was followed by many specialized scientific and business calculators and HP calculators became the standard by which others were judged. Besides outstanding quality and durability, HP calculators use a different input method (Reverse Polish Notation - RPN) that is faster and less error-prone than the algebraic input method used by all other calculators.

Hewlett Packard HP-35
Hewlett Packard HP-35

Hewlett-Packard HP-35

The World's First Scientific Calculator

The HP-35 was Hewlett-Packard's first pocket calculator and the world's first pocket scientific calculator. When the HP-35 was introduced in 1972, most pocket calculators only had 4 basic math functions while scientific calculators weighed as much as 40 lbs and cost $4000 to $5000. The HP-35 cost only $395 and could fit in a shirt pocket. In spite of its small size and price, the HP-35 had numerical algorithms that exceeded the precision of most mainframe computers of the time. The HP-35 featured 10 digit precision, Reverse Polish Notation (RPN) entry, and a 3-level stack. At the time the HP-35 was introduced, many other calculators had poorly designed housings, keyboards, and displays that were failure-prone and crude in design. By contrast, the housing, keyboard, and display of the HP-35 were all carefully thought out. Like all HP calculators, the HP-35 was required to withstand a three foot drop onto concrete on each of its corners and remain undamaged. The HP-35 was a huge success for Hewlett-Packard, with orders in the the first few months exceeding HP's guess of the total market size.

(Photo Credit" Marcin Wichary via Flickr under the Creative Commons license)

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Hewlett-Packard HP-65

HP's First Pocket Programmable Calculator

The HP-65 was introduced in 1974, just 18 months after the introduction of the HP-35. The HP-65 packed a lot more functionality into a calculator that was about the same size as the HP-35. Most keys on the HP-65 had 4 functions, with the additional functions being accessed by the F (gold) and G (blue) "shift" keys or the "f-1" key. Among the added features were the ability to do base conversions between decimal, octal, and hexadecimal, and the ability to directly perform degrees.minutes seconds arithmetic (D.MS+ and D.MS-). The major improvement to the HP-65, though, was its programmability. The HP-65 had 100 lines of program space and used label addressing. It was billed by HP as "The Personal Computer". Programs were stored on magnetic strips. Users could write their own programs or purchase them from HP. One interesting fact about the HP-65 is that it was used by US astronauts to calculate course corrections when rendezvousing with the Soviet Soyuz spacecraft in 1975.

Hewlett-Packard HP-41C/CV/CX - Not Just a Calculator, a Pocket Computer

The HP-41 calculator was introduced in 1979 as a Personal Computing System. The display and keyboard were greatly improved over HP calculators, and the HP-41 really was much more than "just" a calculator. The display was a multi-segment LCD that allowed display of true alphanumeric data, and the keyboard allowed full alphanumeric data entry. Besides that, the keyboard could be placed into "User Mode" which allowed the user to assign any function - either built in or programmed - to any key. HP also sold blank keyboard overlays so that users could customize the labeling to match the programming. Program memory was non-volatile, and pre-written software (application packs) came on ROM modules. The HP-41 didn't come with a built in card reader, but an add-on card reader could be purchased for users who wanted to save their custom written program to magnetic strips. The HP-41 series is probably the most powerful non-graphing calculator ever produced, and there is much more information available than will fit into a few paragraphs. An HP-41 simulator that runs on Windows is available here.

Hewlett-Packard HP-11C

My first "real" calculator...

The HP-11C was the first calculator in Hewlett-Packard's 10C series. Built in functions included hyperbolic and inverse hyperbolic trig functions, probability (combinations and permutations), factorial, % change, absolute value, and a random number generator. The HP-11C also had a limited "User" functionality that allowed the labeled (A - F) gold keys to be assigned user written programs. Compared to other calculators in the 10C series, the HP-11C had advanced programming capabilities. The HP-11C had 63 lines of permanent program space, 20 general purpose registers, and 1 dedicated Indirection (I) register. As programs grew larger than 63 lines, registers were automatically converted into additional program. Each register converted into 7 lines of program space, so if all 20 registers were converted to programming space a program could be up to 203. Programming constructs provided by the HP-11C included labeled addressing (0-9 and A-E), subroutines (nestable to 4 deep). 8 conditional tests, increment/decrement loops, and 2 flags. Indirection (via the I Register) was allowed on STO, RCL, GTO, and GSB instructions, the display modes, and exchange (exchange X with the register indicated by i). The I register could also be used with the ISG (Increment then Skip if Greater) and DSE (Decrement then Skip if less than or Equal).

Hewlett-Packard HP-12C

HP's Premier Business Calculator ...

The second in HP's 10C series, the HP-12C has features and functions designed for business people. As the only "vintage" HP calculator still being produced, it is also the most affordable choice for those wanting to add a vintage style HP calculator to their collection. Instead of scientific and advanced mathematical functions, the HP-12C is geared towards financial calculations. Built in functions include several methods of calculating interest, amortization, internal rate of return, net present value, depreciation, bond price (given desired yield to maturity), yield to maturity (given bond price), and others. Just in case a function you need isn't already built in, the HP-12C also comes with a very thorough user manual with chapters on real estate, leasing, lending, investing, savings, and bonds. In spite of the fact it is over 30 years old, the HP-12C is still the first choice of many financial consultants, real estate agents, and other professionals who work with financial and business data.

Buy at and get FREE SHIPPING...

Hewlett-Packard HP-15C

The Mathematician's Calculator

The HP-15C calculator was designed for math majors and others who needed to do complex mathematical calculations. It had built in support for complex numbers (numbers that include both a real and an imaginary part) and matrix math. Built in matrix operations included basic functions as well as more advanced matrix functions such as determinants, inverse, and LU decomposition. Like the HP-11C, up to 5 keys on the HP-15C could be assigned to user written programs.

HP 15C Limited Edition
HP 15C Limited Edition

Brand New HP-15C Available!!!

Limited Edition version of this AWESOME calculator...

Late in 2011, HP made a Limited Edition run of the HP-15C. If you are a fan of the HP-10 series of calculators this is great news. Now instead of paying $200, $300, or even more for a used 10-series you can get a brand new HP-15C for about $100 from eBay sellers. If you want one, I'd get one now - as I said it was a limited production run and they're already sold out on HP's web site - but still available from several sellers on eBay. I got one and I love it. Now if they'd only make a Limited Edition run of the HP-16C...

Hewlett-Packard HP-16C - A Calculator for Computer Scientists...

In my opinion, the HP-16C was the most interesting calculator ever produced by any company. Designed for computer scientists at a time when programmers were concerned with bits and bytes, the HP-16C could display numbers in binary, decimal, octal, and hexadecimal. Besides just being able to display numbers in various formats useful to computer programmers of the time, the HP-16C could be set to act like just about any microprocessor. Word length could be set to any length from 1 to 64 bits. Math could be performed as unsigned, 1's compliment, or 2's compliment. Overflow and carry flags worked just as they would on an actual microprocessor. The HP-16C even offered 2 different ways to do floating point math, HP-16C native and IEEE standard. Other functions that made the HP-16C useful to programmers included shift, rotate, bitwise functions (AND, OR, NOT, and XOR), bit setting and testing, flag setting and testing, and many others. Truly a unique calculator.

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    • profile image


      5 years ago

      I was surprised to see repacement part of the HP 67 card reader. Thank you very much for this valuable information

    • profile image


      6 years ago

      My first HP was a HP25 i got it in 1976 from my parents, The most facinating experience ever.,. Hard to find in europe in that period , i stil use HP have a little collection HP 25 /hp25c /hp 29c/ hp 11c /hp 15c /hp15C lim edit /hp 42s. My favorite is the HP15c and still using it every day.

    • John Dyhouse profile image

      John Dyhouse 

      6 years ago from UK

      I remember the slide rule, i still have mine! And logarithms, what a nightmare both at school and in the early days at work. We had mechanical calculators for intensive number crunching but they were not convenient for individual calculations. Engineers and scientists hahve it easy these days, LOL

    • profile image


      6 years ago

      my parents bought this brand new

      i remember it being like $100 new of a calculator

    • mycalculadora profile image


      7 years ago

      great lens! looks like it must have taken you many hours!

    • jp1978 profile image


      8 years ago

      Reverse Polish Notation, ouch!

    • grayth lm profile image

      grayth lm 

      8 years ago

      Brings me back to my high school days, thanks

    • capriliz lm profile image

      capriliz lm 

      8 years ago

      This is so like a trip back memory lane. I can still remember seeing one of the early calculators when a student brought one in to the algebra class. It was huge! The advances in technology continue to amaze me.

    • spunkyduckling profile image


      8 years ago

      Interesting info about hp calculators. A tiny one in my pocket would come in handy sometimes. Hmm.. never knew hp meant hewlet packard! Seriously I didn't know that. Thanks.


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