Tacheometry
Today, a set of misunderstandings. The University of Houston presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
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Years ago, I bought old books on old subjects – fodder for these radio programs. I thought this 1951 book on tachometry was about measuring rotational speed – rpm. It sat on my shelf for years. When I finally opened it – just now – Yikes! – it wasn’t about measuring rpm at all. It was about surveying!
Then I looked closer: The title had an extra letter – TachEometry, not Tachometry. What in the world is tacheometry? Well, the word comes from two Greek words: tachys metron, for quick measurement.
Nothing about rpm. It’s about a technique used in land surveying. And here the plot thickens further. You see, I worked on surveying crews in my summers during college – before this book came out. And I’d never heard of tacheometry.
It turns out that earlier surveyors measured distances with a metal chain – linked metal rods that folded up. We had, by the 1940s, perfected long metal tapes, etched with feet and inches. We’d coil them up and sling them over a shoulder. Then we’d stretch them out to measure distances. They were far more accurate than those old chains.
A surveyor’s “Gunter’s Chain” once used to measure distances. (Image courtesy of Wikimedia.)
Tacheometry was an optical shortcut for measuring distances – almost as accurate as those old chains. And sometimes easier to use. It used an instrument called a theodolite for reading angles -- that, and a lot of very fancy trigonometry. And here’s a whole book on its use.
Typical page of Redmond’s book, Tacheometry. (Image courtesy of Wikimedia.)
The author’s Preface says that he began the book ten years earlier. (That would’ve been just as metal tape was perfected.) He even admits that his book might better serve less advanced countries. He seems to realize that it was already a dinosaur.
Maybe he was slower than most in recognizing his own nostalgia. Meanwhile, change is always upon us before we fully see what’s happening. Just as tacheometry was long gone before this book came out. So too, today’s surveyors, with their lasers, global positioning, and more ... They have no idea what our old metal tapes were all about.
I said this would be a set of misunderstandings. And each stems from the way our technology moves faster than our understanding. That, in turn, is nourished by nostalgia. How I love the old surveying instruments that we used when I was young.
Those transits, levels, and metal chains – they were equipment used by a young George Washington. And they were, mostly, still the stuff of my own youth. Here is just one more past. Like so many pasts, it’s hard for those of us involved to lay aside – especially in this rapidly changing world.
And that is just the kind of thinking that we embrace at our peril today.
I’m John Lienhard, at the University of Houston, where we’re interested in the way inventive minds work.
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F. A. Redmond, Tacheometry: A Practical Treatise for Students and Surveyors: London: The technical Press Ltd. 1951
This episode first aired on November 25, 2025.