No certified marathon is 42.195 kilometers long. The rules do not allow it.

A road course is measured by one person on a bicycle. First they ride a straight, steel-taped stretch of road four times, to learn how many clicks of the counter on the front wheel make a meter that morning. The answer is inflated by one part in a thousand. Then they ride the course along the shortest line a runner could legally take — every tangent cut, every corner hugged — and ride it again. The two rides must agree within eight hundredths of a percent, and where they differ the shorter one is believed, and the finish moves until it is satisfied. Last they ride the taped stretch four more times, because the tire has warmed across the day, and whichever constant makes the course longer wins.

Every fork in the procedure breaks the same way. A certified marathon is at least 42,237 meters, and the extra 42 are not the error. They are the method.

The counter is a Jones Counter, built by an IBM engineer near Binghamton after his first race, advertised as twenty kilometers, came up a mile short on his car's odometer. His nine-year-old son assembled them for a dollar apiece.

The method has teeth. In December 1984 someone re-rode the 1981 New York City Marathon and found it about 150 meters short. Alberto Salazar's 2:08:13, the fastest marathon anyone had run, stopped being a record three years after the fact. Nobody had cheated. The course had been short all along.

I like that the fastest people alive run a distance fixed by someone at cycling pace, hugging the curb, pretending to be greedier than any of them. Whatever the winner ran, the bicycle ran it first, and farther.

The number your weather app calls "feels like" has never described you.

For most of a century it described a bottle. In 1940 Paul Siple and Charles Passel hung a small plastic cylinder of water from the roof of an Antarctic hut, level with the anemometer, and timed how long it took to freeze. What they published in 1945 was a cooling rate in kilocalories per square metre per hour — a four-digit number, not a temperature. Somebody else converted it into the friendly negative one a radio announcer could read.

That held until 2001, when a joint American, Canadian and British group replaced it. The current index models heat leaving a bare adult face turned into the wind, walking into it at 3.1 miles an hour. The wind comes off the standard anemometer at thirty-three feet and is scaled down to five feet, where a face is. The sky is clear and it is night, so the sun contributes nothing. Twelve volunteers, six men and six women, spent ninety minutes at a stretch on a treadmill in a chilled wind tunnel in Toronto with thermal transducers taped to their foreheads, cheeks, noses and chins.

The numbers came down hard. St. Louis reported 69 below on 20 January 1985; run that day through the current formula and it is 48 below.

None of which made the number about you. You have a hood up, you are standing still at a light, it is two in the afternoon and the sun is out. The old index at least sounded like an instrument. This one sounds like a person, and there is a particular one it means: bare-faced in the dark, walking into the wind at exactly 3.1 miles an hour.

The box an expensive object came in is rarely allowed to become trash at the same speed as the object becomes ours.

A phone, watch, or pair of headphones leaves its box in seconds. The box then waits for years. It occupies the back of a closet with its precise recesses empty, too finely made to hold anything else and apparently too important to discard.

Packaging is supposed to be temporary architecture. This kind is too competent at its job: dense board, exact tolerances, a lid descending on a trapped cushion of air. Throwing it away feels less like clearing debris than discarding part of the purchase.

We say we keep it for resale, moving, or the warranty. Sometimes that is true. Mostly, I think the box guards a more flattering possibility — that our choices remain reversible. The object may be scratched and absorbed into daily life, but its box preserves the day we chose it as a clean decision we could still undo.

I like the moment the box finally goes. It is not decluttering. It is an accession ceremony. We stop treating the thing as merchandise and admit it has joined the household. The return window closed years ago. Ownership happens on recycling day.