The Daily Shoot 95

15 years ago

For Thursday 18th February (#ds95), we were asked this: "Frames outline the focus of a subject. Make a creative photo with natural framing: windows, doors, trees, borders, etc." I really should have spent more time on this, but, due to a lunchtime appointment (plus dental appointment in the morning), I didn't have enough time to do anything really good. Maybe I'll find a subject to photograph this weekend for my own personal satisfaction.

So, I decided to merge two topics in one. Yesterday I received a very clean, nicely-looked-after HP-35 calculator. Quick bit of history: the HP-35 was the first pocket scientific calculator, released at a time — 1972 — when scientific calculators were the size of bulky laptops and pocket calculators had just the basic 4 operators. My copy is what you might call an example of version 3.0 (there were four versions in all, before it was discontinued). The HP-35 essentially hammered the final nails into the coffin of the slide rule.

To celebrate, I decided to quickly snap the HP-35 framed by two slide rules from my collection: a fabulous German Faber-Castell Novo Duplex 2/83N, possibly the largest, prettiest, most-complete slide rule ever made (it has 30 scales, or 31 if you count the two C scales as separate) which was manufactured at roughly the same time as the HP-35; and a K&E Deci-Lon 68-1100, the largest slide rule produced by the American Keuffel and Esser company (26 scales) from about 10 years earlier.

Quick notes. The HP-35 — so called because it has 35 keys — uses RPN (Reverse Polish Notation) entry, a 4-level stack with automatic lifting and dropping, trigonometric functions (sin, cos, tan, plus inverse), transcendental functions (log, ln, e^x, x^y), single memory register. 10-digit mantissa with 2 digit exponent, although it used 11 LEDs to display the mantissa since the decimal point always occupied one of the digit positions. The weirdest key is possibly the x^y key: to use it you entered the exponent first and then the number that needed to be raised to that power, the opposite of the way you'd normally think about it. The main reason for putting it that way around is that there was no dedicated 10^x key, so to find the anti-log of the currently displayed value (the x value), all you had to do was type 10 x^y. Angles for the trig functions were always in degrees, so I suppose you got used to converting radians to degrees "by hand", which, because of RPN, was simple (π × 180 ÷).

A lot of work went into the design of the keyboard: we can see keys of four different colors and contrasts (high contrast for the main keys), the colors/contrasts providing different groupings; three different sizes for the keys to further emphasize the groupings. The keyboard itself is slightly angled to the user, which also helped to hide the bulk of the calculator. All this attention to design was very different from the other pocket calculators of the time.

To differentiate the versions of the HP-35: version 1.0 had a dot to the right of the power switch, so when that was ON the dot was red (this is the so-called red-dot version); version 2.0 lost the dot; version 3.0 added the identifier "35" to the front panel of the calculator (so it read "Hewlett-Packard 35"); version 4.0 modified the upper part of the keyboard so the key legends were embedded into the keys themselves rather than being printed above the keys.