"Don't know what a slide rule is for"

In October 1980 I was a month into my my seventh year of teaching.  I was teaching social studies at John F. Kennedy High School in the Bronx and the fall presidential campaign -- Jimmy Carter running for re-election against Ronald Reagan -- was an important part of our curriculum.  In those days political cartoons were always on the US History and Government Regents Examination so we introduced them in class from time to time.  It turns out that the visual language of those cartoons is anything but universal and so the tropes and memes have to be taught.

That need for teaching was glaringly apparent on this day.  I cannot find the cartoon, so I will have to describe it.  It showed Carter and Reagan debating.  Carter had a chalkboard covered with complex equations and cryptic symbols, while Reagan's chalkboard simply showed a smiley face.  My students were able to see that the cartoonist believed that Carter was overly complicating things and speaking over the voters' heads, while Reagan was over-simplifying the issues.  What they could not interpret was the device Carter held in his hand: a slide rule.  They had never seen one before; they didn't know what it was.

I graduated high school only ten years earlier, in 1970, when the slide rule was a clear marker of the science student and the engineer.  Not all my classmates knew how to use one.  Hell, I suppose most of them didn't even know what a slide rule was for. (See the great Sam Cooke's song, "What a Wonderful World.")  What I liked about multiplying and dividing with a slide rule was the constant reminder that you were approximating your third digit and that was the best you could measure anyway.  After all, I measure the distance from my home in the Bronx to my daughter's in Brooklyn in miles, not feet or inches.  Anything more than miles is a false precision.

The slide rule was a big deal in my house, too.  My dad was an engineer.  When he was discharged from the US Navy in 1946 and returned to college, his GI benefits didn't help much with tuition, because City College was still free!  But those benefits allowed him to purchase a top-of-the-line Keuffel and Esser slide rule for the equivalent of a week's pay, $25.  It was always near to hand when he was working, so I was happy to learn how to use one and get my one of my own, even if it was inexpensive and made of plastic.

The complete disappearance of the slide rule in just ten years, to the point that teens didn't even recognize it is pretty astonishing.  People today know what CD's are, even though it has been fifteen years since the first iPod came out.  People still go to the movies seventy years after the popularization of home TV.  But a slide rule is an antique, a piece of technical arcana.  It has been erased.

That year, when I was a high school senior, the first "pocket" calculators came out.  One of my classmates, the only child of well-to-do parents, got one.  It was what we later called "four function," meaning it could add, subtract, multiply and divide.  By the time of that Reagan-Carter cartoon in 1980 you could buy such a thing for under $5 and actually fit it in your shirt pocket.  The calculator my classmate had in 1970 sold for about $500, was about the size of a modern tablet (9"x5"), and weighed a lot.  And $500 in 1970?  More than the $2000 cost of a laptop today.  I bought my first used car then for $300.

I couldn't imagine why anybody would want such a thing.  But I have been remarkably blind to the emergence of the calculator all along.  I'll permit you another opportunity to laugh at me.  In 1983 or 1984 I took a year of college physics because I felt like it.  When it came time for the first exam I saw that all my classmates were carrying calculators.  I smiled, because I was absolutely certain the professor would forbid us to use them.  These were programmable devices; you could save all the formulas we were being tested on right inside the calculator.  Why would they be allowed in an exam room.  But I was the idiot: they all got to use their calculators while I was left doing all my computations with a pencil.

When I was an assistant principal for Math and Science at Monroe Campus in 2001 all our ninth graders had to learn how to use a graphing calculator.  They were encouraged to use it on their Regents exams and we had to provide one for each of them in class and during the exam.  But when I say "learn how to use" that is exactly what I mean.  They were not intuitive at all and required the mastery of a particular set of key strokes.  I remember one principal actually scolding parents for buying their children $120 shoes instead of that $100 calculator.  Her position was that if they didn't practice with it nightly, on each homework assignment, then they would be at a profound disadvantage on the day of the test.

Today (and for the last ten years) I have all the functionality of that calculator in my pocket at all times.  It is built into my telephone, along with a high-definition video camera, a GPS app, a music player, a portable TV and all sorts of other things.  It is a much easier calculator to use than that TI-82, but I suppose that the kids still can't bring it into exams because it also allows them to text answers to one another.  In any case, I have seen electronic miniaturization erase the slide rule, replacing it with the pocket calculator, and now -- almost -- erase that calculator, too.

But I still think that one think has been lost, and it has to do with the false precision I mentioned above.  I keep on seeing people who mistakenly think that all those decimal places we get, on calculators or phone apps, actually mean something.  In 1996 I saw a student presentation by a tenth-grader on the  epidemiology of sexually-transmitted disease.  For her study she inferred the number of STD's among teens in a particular census tract in the Bronx.  She multiplied the CDC's estimate of teen STD rate by the number of teens in that tract in 1990.  I will ignore now (I did not then) the conceptual flaws in this method.  But my other problem was that she hit on a number of cases with decimal places extending to the limit of her calculator!

Let me clarify.  She confidently announced that in the neighborhood of the school, there were 637.1501792 teens with STD's.  (No, I don't remember the exact number, but you get the idea.)  I questioned her about her precision.  I asked her what .1501792 of a teen looked like.  I asked her what .1501792 of an STD was.  I even asked her why she was certain it was 637.  She grew increasingly angry with my questions and simply redid the computations on her calculator and angrily shoved the display in my face.  She was a bright girl.  And, yes, she was nervous about presenting her work.  She was even more nervous about my challenging it... after all, her teacher had accepted it and had approved it for presentation, so this was hardly her fault.

But the underlying problem remains. I can use a stopwatch (also in my phone!) to time myself walking a measured mile and conclude that my speed was 160.9344 meters/second.  But was that mile measured with that degree of precision?  Was the starting line itself marked off thinner than a micrometer?  Did I accurately start my timer when the leading edge of my finger crossed the plane of that (extremely thin) starting line?  How about when I crossed the (equally thin) finishing line?  Was I a millisecond fast or slow in hitting the start and the stop on the timer?

Three digits.  That's what a slide rule could handle.  I think that's also a reasonable standard for most measurements.  I don't mourn the loss of the slide rule.  I like my phone's calculator.  I like its graphing calculator, too.  But I always think about just how quickly that slide rule disappeared.  And I do miss those three digits.