The Museum of HP Calculators

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Full Name (family, given): Hayden, David
Account Name: David Hayden
Contact: David Hayden
Location: Crosswicks, New Jersey, USA
Entered: 21 Feb 2010, 7:57 a.m.

One day when I was about 13 we went to dine at a family friend's house. The father had recently bought an SR-52 calculator from Texas instruments and he showed it to me. I spent the rest of the evening in his study playing lunar lander. He let me borrow the calculator and I learned how to program it, figured out how lunar lander worked and basically fell in love with programming. I think I wrote a program to find prime numbers or prime factors on that calculator.

My brother bought an HP 25C shortly thereafter and I really liked it. I talked my father into buying me a 29C about a year later. It helped me enormously in my studies. This was around 1977 or '78 and it was a time of great change. Textbooks still had log and sine tables printed in the back, but everyone used a calculator instead. Not a single student owned a slide rule or even knew how to use one. The most popular calculator was the TI-30 which was a scientific calc and cost about $30. Only a few of us had programmable calculators.

I clearly remember the bus ride from Lawrenceville to Princeton NJ one day when an older student told me about HP's revolutionary new calculator. It had an alphanumeric display so when programming, you could see the name of the instruction instead of the keycode. The display was LCD so you could see it in daylight. Lots of continuous memory and expandable so you could add more. You could even get a card reader, printer, cassette tape storage, etc. By the time we got to Princeton, I NEEDED it.

I scraped and saved and bought an HP 41C by mail (it was cheaper). It arrived one cold Saturday and I spent 12-14 hours going through the manual cover-to-cover. A card reader, memory modules and printer followed. I wrote many programs, submitted several to the HP Users Library and one was even featured in the HP journal.

By now I was hooked on computers. In college I studied Electrical Engineering, concentrating in computers. I replaced the 41C with a CV in 1983. I became a professional programmer (C and C++ mostly).

I used the 41CV exclusively until around 2005 when my daughter needed a graphing calculator for school. I was only vaguely aware of such things, having lost touch with advances in calculators. I decided to see what HP had been up to in the past 30 years so I bought a 50G and started playing around with it.

Today I own both versions of the 48gii, a 50g and a 39gs. I program them in UserRPL, sysRPL and C with HPGCC and I suspect that I"m the only one who's gotten HPGCC working on the 48gii because there was a bug in the code that creates objects, so there was no way to push results back on the stack.

I am the author of the HPObjects library available on This library lets C programs parse and create any type of HP object in a consistent way. I am also the author of a C++ sudoku solver that can solve any Sudoku puzzle on the 50g in less than 1/10 second.

When I'm not programming for fun or profit, I enjoy kayaking and indoor rowing. I'm also on the Board of Trustees at two schools and a swimming club. I live in New Jersey, which is on the East coast of the USA. I'm located about half way between the cities of Philadelphia and New York.


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