I found this old ruler packed in a box of things from my childhood room. It looks like something one of my parents brought home from work, and that I probably nabbed to draw the straightest lines my four-year-old fingers could manage. Rediscovering it now, and looking past the groovy 70’s industrial styling, I noticed something peculiar.
From a distance, this Uarco ruler looks like a typical specimen of the common American ruler, with inches on one side and centimeters on the other. On closer inspection, it becomes clear that this ruler holds no truck with Système International. There are five different scales on this ruler, and not one of them is in metric. They are:
- Inches divided into 1⁄16″ increments, classic and traditional.
- Tenths of inches, presumably for making 1:10 scale drawings.
- Inches divided into 1⁄6″ and 1⁄12″ increments, for making 1:12 scale drawings.
- Then, considerably more odd, lines every 5⁄32″. The spaces are labeled from 1 to 43, then they skip a space, and then they keep counting from 45 to 100. The numbers 1 to 45 are also repeated on the right-hand side, right under 45 to 90.
- Last there is a set of lines spaced an inch apart that count up by 150 per line. This row is marked with the label (CARDS), which happens to be the key to unlocking the 5⁄32″ mystery.
I love esoteric units of measurement, and this ruler introduced me to a new one: instead of millimeters or miles or parsecs or picas, this ruler lets you measure distances in stacks of punch cards. The conversion is about 150 cards to the inch (the nominal manufacturing thickness is 0.007″ ± 0.0004″ per card, specified in decades-obsolete ISO and ANSIstandards that will still set you back $30–70 if you’d like to read them today).
How does that relate to 5⁄32″? I guessed that it was for measuring the columns in punch cards, but that didn’t seem to add up. I’ve never actually used a punch card, but in all of the legends of the times of yore, each card had 80 columns (a property that lingered on in command-line interfaces well after the sell-by date). This ruler is numbered from 1 to 45 twice, sort of, with no special attention given to column 80. It also turns out that the columns on IBM punch cards are slightly less than 3⁄32″ wide, so much too narrow.
If the ruler wasn’t for IBM punch cards, maybe there were alternative punch card formats? It turns out that one of the precursors to the ubiquitous IBM card was the 45-column “Hollerith” card, which used columns spaced precisely 5⁄32″ apart! The cards are named for Herman Hollerith, who invented tabulation machines to speed up the processing of the 1890 US census (spoiler alert: the population tally was 62,947,714, and then all of the records caught fire). Using machines to count up results automatically was pretty clever for its day, decades before electromechanical computers (though also decades after Charles Babbage and Ada Lovelace were dreaming about sophisticated card-driven computation engines, so it’s not like the idea hadn’t been kicked around before).
He built and sold different versions of these machines through his company, the Tabulating Machine Corporation, that later merged into the Computing-Tabulating-Recording Company, that was later renamed International Business Machines.
In 1928, four years after adopting its new name, IBM released a new kind of punched card that used narrow rectangular holes instead of the old circular ones. The thinner punches let them squeeze 80 columns onto each card instead of just 45. IBM quickly stopped making machines for the 45-column cards, and doubtless assumed that the obsolete format would soon disappear. They were wrong.
You see, IBM was granted a patent on this new “square hole” technology, which made it expensive for competitors to develop compatible machinery. Instead of coughing up the licensing fees, rival Remington Rand figured out a new encoding for the old 45-column cards that doubled the information density (effectively turning them into 90-column cards!) while still using the same old round holes that Hollerith had started with. This format was given a boost in 1950, when Remington Rand bought early mainframe manufacturer UNIVAC, which was redesigned to take advantage of the information-dense “90-column” cards. Some of those machines remained active in government and military installations well into the 1980s. They’ve probably all been replaced with a couple of Apple ][’s by now, but I like to think that there’s still a UNIVAC plunking away in a bunker somewhere, chewing through frayed and yellowing Hollerith cards to tabulate payrolls for a nearby army base.
So this ruler was designed for an office that dealt with UNIVAC mainframes instead of IBM big iron. With it you could estimate how many cards were in a program, measure scale drawings of circuit boards or inch-to-the-foot blueprints, and quickly determine which column on a card might have been spindled or mutilated. I ended up reading a lot more about this than I expected, but I still have a few questions left. It’d be nice to know roughly when it was made (the Computer History Museum has a similar ruler in its collection, but doesn’t list any dates). I’d also like to know what the precisely spaced holes are used for, or what the crossing dashed lines on the black side might line up with. And last, I need to ask my parents if either of them ever actually used it to measure any real-life punch cards.