Global Skywatch

Ted’s essays

analog calculators

In this age of converting everything to digital, bits, bytes and button pushing, my recent trip to a beginners’ long-range shooting school (see my first 1K) brought the power of slide rules back into my world. I am also [re-]discovering the beautiful metric system of measurements.

The normal, average, mundane, commonplace answer to everything today is “I have a computer that does that”. Substitute “smart phone”, calculator or other electronic alternative to knowing how to actually do stuff and you have the answer to 99.9% of the computational questions asked today.

I am not going to conjure up ways in which that dependence on electronics could fail us. Needless to say there are times, places and circumstances where it could. But that is only a part of my motivation to gear up for analog calculation.

Today, four tools arrived at my estate that made me a bit giddy with the excitement of them all.

On the right is the Mildot Master that reintroduced the slide rule concept into my brain. Numbers on the outer sleeve list milliradians on one side of the opening and an arrow points to target range on the other side of the opening. Move the slide until the target size lines up with how many dots it covers in your scope. If a target 40 centimeters tall covers 2 dots on your scope, it is 200 meters away.

As fast as you can look at it, your answer is in front of you.

Oh yeah, that calculation above is by special order. Their basic slide insert uses mils, moa, inches and yards so those eschewing the metric system can have their convoluted system calculated for them.

That being only a part of the calculus necessary, shooter and spotter need to turn that bit of information into hold-off, hold-over, or settings on the scope’s windage and elevation knobs. We need charts or calculations to do that … and certainly calculations are going to be needed to make those charts.

Dad says that anyone who can’t use a slide rule is a
cultural illiterate and should not be allowed to vote.

from Have Space Suit Will Travel by Robert A. Heinlein (1907-1988)

Having slide-rule technology already in the forefront of my mind, I thought possessing one of them would be handy to have for simple multiplication, not to mention other calculations I used to be able to do with them.

As always, the Internet is our friend. I found PLENTY of choices and picked up a couple of inexpensive slide rules… unwilling to commit too heavily in case this is a fleeting fancy of the moment.

Larger slide rules are easier to read in greater detail, while the small ones specialize in the important feature of being with you, but trade off precision. Since they have not been manufactured in a generation or two, new ones are unobtainable. Used ones vary in quality and condition.

I picked out a standard 25cm one and pocket sized 15cm (notice how I slipped the metric system into our conversation ๐Ÿ˜‰ ). A little dressing up with a fine file, beeswax, silicone spray and attention delivered two nicely functioning standard sliderules … plus the magical, rare FLUOR one.

The Sliderule Museum has a wonderful tutorial on how to use them. Shock-of-all-shocks, my computerized spell checker had to be taught that sliderule is a word. I will be renewing my understanding of slip-sticks over the next little while.

This neat little quip below from their tutorial emphasizes the disadvantage suffered by a generation who punch numbers into calculators by rote. If their calculator tells them the school they attend is 5,473,395 miles away from their front porch, they simply write that answer into the appropriate space.

…The curse and blessing of modern calculators is that this type of thinking is no longer necessary or encouraged by educators. Students just hit buttons and copy down what is on the display. Of course the fact that most of the digits in the display of a calculator is useless noise does not bother most students. Modern students are not challenged to judge whether or not the calculator’s result is in the right range, and errors can be propagated…

My real find in this foray was the conversion calculator from the olden-days, apparently built for the mechanical engineers of the Fluor Corporation. Force, pressure, energy, power, length, area, volume and mass all converted with inner-slide on outer sleeve from mathematically gorgeous metric to the stupid, convoluted inches, feet, yards, quarts, psi, foot-pounds and all those other rats nests of measurements. Heck, it even does Centigrade, Fahrenheit, and Kelvin conversions.

Twenty one windows in an 8cm by 215mm slick cardboard sleeve contain tables that would fill an engineering pocket book. I don’t think I can find an individual in the real world who could explain the relationships in all of these windows.

Yet this antique tool not only exists, I HAVE ONE!

Better still, it is only a part of my [growing] sliderule collection.