RPN (Reverse Polish Notation) programmable calculators from HP, such as the Voyager series HP-11C and HP-15C, have been around since the early 80’s. It was a cool and powerful scientific calculator that was too ahead of its time.
I used to be a proud owner of one original HP-15C while studying engineering at the institute between 1984 and 1989, but sadly, it got lost in 1989 via a flash flood due to a strong typhoon. So, during the board examination, I had no choice but to painfully switch and use an algebraic notation Casio calculator instead.
You could not easily buy this type of calculator (made in the USA) from shops in the Philippines back then. I remember there were only two of us, students at the institute, who owned this kind of calculator; the other classmate, however, had the HP-11C model. We were the only ones who could borrow each other’s calculator when we had forgotten to bring it. Other classmates who attempted to borrow it would hurriedly turn around and exclaim in puzzlement, “Hey, why is there no = button in your calculator? ”
The HP-15C has built-in matrix (up to 8×8) operations for both real and complex numbers, which greatly helped me in higher math subjects, especially circuits and network analysis. Solve key (finding the roots for both algebraic and transcendental equations) and integration key are cool standard features as well.
A couple of years later, after graduation, while working for Philips Electronics and Lighting in the early 90’s, I had the opportunity to travel to Singapore for training. One weekend, while strolling through the shops, I found a store that sells HP calculators, but unfortunately, there were no more HP-15Cs available. I learned from the attractive saleswoman that HP had already stopped manufacturing this model in 1989. I ended up buying an alternative model, which was the HP-32S II (made in Singapore), also an RPN type. This calculator has been with me until now and is working fine about 30 years later. Since these powerful calculators are now vintage, the pre-owned, hefty price range on eBay is around $150 to $300.
Last year (2023), I was finally able to buy an HP-15C Collector’s Edition from an Australian online store. Excitedly, me and my wife drove to the local post office to collect the parcel on the day we received a call that it had arrived. I was surprised to find out after opening the box that this time around, it was proudly made in the Philippines!
Thank you for bringing back the HP-15C with an improved and faster processor (approximately 30 times faster than the original); it was also a very timely release for my graduate school maths. I tested the integration of the transcendental equation (please see below) and compared the run time with the other brand of calculator. The HP-15C is blazingly fast and has left the other brand in the dust!
Once again, today, it is still a scientific calculator that is way ahead of its time.
The above equation took only 10+ seconds to integrate in HP-15c, while another brand took 1.36 to 3.23 minutes to integrate the same equation.