There is something seductive about the sharp edge of precision. Time sliced into nanoseconds or soap that is 99.44% pure; satellite navigation systems that can pin down position to a few square yards or sound systems that sing in clean digital tones; precision cars, razor blades, haircuts, paint colors, personality profiles. Whether it's IQ scores, TV ratings or the skill of Olympic ice skaters, we attach a precise number and, presto, we think we hear the clear ring of truth.
Precision validates our senses, adding trust, a sense of surety. "Precision is everything that ambiguity, uncertainty, messiness, and unreliability are not," writes M. Norton Wise, editor of "The Values of Precision," a collection of essays exploring the "explosion of everyday precision" that defines the modern world. "How did numbers come to represent the cutting edge of modernity?" asks Wise. "It was not always so. . . ."
Exact measurements are relatively recent inventions that emerged in the late 18th century, largely in the physical sciences. But above all, they emerged from culture. The history of precision is not about numbers or instruments or machines so much as it is about people and the societies they build. It is about what people value, how they value it and how they agree on values.
Consider: Just why would anyone want or need to know precisely how many people live in a nation's borders, how much money they earn or what they do with it? How far is it from here to there? How much has the climate changed over the last 100 years? How smart is someone or how beautiful? How much a hunk of something weighs or how much liquid fits in a bottle? What's the probability that someone will die at a given age? How much is something or someone worth? What's the size of a brain or the length of a meter? The fact that we bother to count tells us that these are the kinds of things we care about.
At root, the search for precision is an intensely human enterprise and as such can't ever be, well, precise. It reminds us, over and over, that "numerical values attach to things that are valued," in Wise's words. It's a disturbing (if imprecise) thought: If we haven't yet attached a precise number to something, we probably don't value it much.
Luckily, this volume rejoices in the many levels of ambiguity present in the history and practice of precision. "We intend to open topics rather than to close them," writes Wise in his preface. Based on a series of papers and discussions that took place in 1991 and 1992 under the auspices of the Princeton Workshop in the History of Science, the collection presents historical case studies by a variety of authors, including Theodore M. Porter of UCLA and Kathryn M. Olesko of Georgetown University.
Curiously, precision is not an objective enterprise. It requires consensus among people, an often tortuously negotiated social contract. Consider, for example, what it means to make a precise measurement of someone's height. What makes the measurement exact?
First, of course, the measuring tape needs to be of standard specifications calibrated correctly down to the desired level of detail: let's say, 1 millimeter. Then it has to be anchored in the right place, and the resulting measurement has to be read without error. Another person making the same measurement should get exactly the same result.
The result of the measurement is a number. What does it mean? That's very hard to say. In the first place, measuring anyone's height to a millimeter is meaningless because most people shrink an inch each day (and gain back the inch at night) simply because of the pull of gravity. So it makes about as much sense to measure height to the millimeter as it does to measure the distance from New York to L.A. in inches. While you're making the measurement, the ground can shift.
But there's more: The temperature of the room (and therefore the length of the tape) can change. The person being measured can shift or slump. The person doing the measurement can get distracted, slip, tremble or lie.
Moving from home to the laboratory, the same kinds of caveats apply. Precision within the laboratory requires "an extensive set of agreements about materials, instruments, methods and values that reach out into the larger culture," writes Wise, "[R]eliability is never a matter simply of a reliable instrument. It is also a matter of people judged to be reliable using methods that display their reliability."