Humans are animals that measure things. Call us Homo mensura. We have a compulsion to quantify, and for millennia we’ve been inventing new ways to go about it. For anything you can think of, there’s a device to measure it—from sphygmomanometers to spectrophotofluorometers. And of course nowhere is this more true than in science. Well, science and baseball.
Physicists build models to explain how the world works. It might be an equation, like the ideal gas law: PV = nRT. This tells us, for example, that if you double the temperature (T) of a gas, all else equal, its gas pressure (P) will double. But to see if the model is legit, or at least useful, we need to get some real-world values and check whether the equation holds. Modeling and measuring, measuring and modeling—that’s science in a nutshell.
Of course, today we have some pretty fancy instruments for this. But I’m going to let you in on a little secret: With all of our cool tools, measurement still comes down to either comparison or counting. In that sense, it hasn’t changed much since Noah built his ark from a spec sheet in cubits—the length of a human forearm from elbow to fingertip. Let me show you what I mean.
Measuring Length
I’m going to start with a measurement that everyone has used at some point: length, or distance. It seems simple, right? If you want to know the length of a pencil, you lay it down next to a ruler. There, it’s 18.7 centimeters. (Yeah, in science we’re on that side of the ruler.)
Photograph: Rhett Allain
What you’re doing here is comparing the length of a pencil and the length of a ruler side by side. (Of course this brings up another issue: How do you know if that ruler you bought online is accurate? That’s a whole other discussion about standards. We can save that for another day.)
The nuttiest comparison measurement ever took place in 1958 when a group of MIT undergrads set out to find the length of a bridge over the Charles River. They had the shortest member of their group, Oliver Smoot (5′7″, or 170 centimeters), lie down repeatedly, marking the sidewalk with chalk, all the way across, and found the bridge to be 364.4 smoots, “give or take an ear.”
(You can’t make this stuff up: Smoot went on to become head of the American National Standards Institute and later the International Organization for Standardization. The definition of a smoot was revised in 2015, when photographic evidence revealed that at age 75, his stature had diminished by 3 centimeters.)
Anyway, it turns out that measuring length or distance by comparison is the most common method used in analog devices.
Other Distance Measurements
For example, what about time? One of the oldest timekeeping devices is the sundial, which in its familiar form was invented by the ancient Greeks. It has a triangular blade, called a gnomon, and a flat disc with numbers around the circumference for hours.
Photograph: Rhett Allain