Editor’s note: Also see Ken Coffman’s blog: The HP15C returns as an iPhone app.
With the emergence of hand-sized computers, calculators have lost some of their former prominence, yet they continue to be a convenient and important engineering tool. Electronic calculators have been around since the early TI high-volume calculator ICs which were selling in the 1970s for a few US dollars and at a hundredth the price of 8-bit microprocessors such as the Intel 8080 or the Motorola 6800. Then Motorola designers Chuck Peddle and Will Mathys relocated from the arid zone of Arizona to MOS Technology, in colder, wetter Valley Forge, Pennsylvania, and developed the $20 (in unit quantity, at introduction) 6502. Later, this site produced Atari computers with 6502 microprocessors.
As we marveled at the low introductory, single-unit price of the 6502 in the mid-70s, an IC production engineer at Tektronix pointed out that the chip size of microprocessors and calculators were comparable, and that in volume, they should have comparable prices. They do now, and for quite some time, calculators - especially scientific (in distinction from grocery-store) calculators - have been implemented as special-purpose or application-specific computers. Scientific calculators now sell for a few dollars - not only the IC but the entire unit, including display and keyboard, battery holder, and in some cases, solar cell. TI continues to be a major supplier of low-cost scientific calculators, though various Asian brands such as Casio have also established a place in the market.
The Venerable HP 45
In the 1970s - the calculator decade - HP also made their mark with the introduction of the HP 35, and shortly thereafter, the HP 45, the first scientific calculator of great impact, predating TI scientific calculators. An HP 45 is shown below, over 40 years later, in front and rear views, with some accessories.
The manual (not shown) was also included in the purchase of the $400 US calculator. The carrying case had a loop on the back for carrying the HP 45 on a pants belt. (The nerd look was more in fashion then.) The security cradle was optional but practical; these were not $15 commodity-grade calculators!
One of the major differences between the HP and TI calculators was the number entry format. TI used the familiar infix notation of mathematics and HP used postfix or RPN (reverse Polish notation, named after the Pole whose name was too hard to remember). Which is better? The infix format has the familiarity of math notation but requires more button pushes involving parentheses to enter a numerical expression. RPN is stack-based; the HP calculators had a four-number stack. Instead of pushing 3 + 4 = as on an infix calculator, you pushed the sequence: 3 ENTER 4 + . The ENTER key pushed the 3 down the stack, allowing the 4 to be entered on top. Then + added the top two stack numbers and left the sum on the top of the stack, which was always displayed. After a user became familiar with these slight differences in numerical entry, the RPN calculator was more efficient, with fewer key strokes. It also was more observable with stack operation keys (shown in a closer view below) such as swapping the top two stack items (upper-left) or rolling the entire stack down (and around to the top) (upper-right).
The ENTER key was larger, as it is on a QWERTY keyboard, and used often in pushing numbers on the stack.
The display consisted of red seven-segment LED digits of small size in 14-pin DIP packages having 5 digits each. These LED arrays were also made by HP and were attractive components in themselves for small instruments, though I do not recall seeing many in other than HP calculators. Radio Shack sold them, expensively packaged, so that it was possible to replace faulty displays. However, I do not know of any display failures, though in Tektronix engineering, most engineers and many technicians had HP 35 and HP 45 calculators.