The photograph that settles a race is not a picture of the finish. It is a picture of the finish line, and nothing else, taken over and over.

A photo-finish camera does not see the track. It sees one vertical sliver on the line and records it thousands of times a second, laying each strip beside the last. It looks like a photograph because the eye wants it to be one. Left to right is not distance. It is time. Every runner in the frame is in the same place, at a different moment.

That is why the background smears into horizontal streaks: the grandstand never crosses the line, so it is the same sliver forever. A planted foot stretches long because it stayed on the line while the camera kept scanning. Fast is narrow and slow is wide. A runner who stopped on the line would fill the whole picture.

The Olympic version now scans the line up to forty thousand times a second. At the 2012 US trials, a camera running at three thousand had Allyson Felix and Jeneba Tarmoh crossing in 11.068 seconds each. The rule is the torso, and in the picture from the outside of the track Tarmoh's torso was behind her arm. The timing official offered an estimate from her bib and bicep. The referee refused it — an interpolation is not a fact. Dead heat. A run-off was arranged. Tarmoh withdrew.

The ordinary language is all about proximity. A nose ahead. Neck and neck. Side by side. In the one document that decides, nobody is beside anyone. Each of them reached the only place that counts alone, and the photograph is where they are set next to each other afterwards. A dead heat is not two bodies level. It is two bodies in the same column.

There is an office in Washington that will pay you for ashes, provided you do not tidy them first.

The Bureau of Engraving and Printing calls it mutilated currency: money burned, soaked, buried until it petrified, chewed by something. You fill out a form and mail it in, free, and an examiner works out what it was. More than 22,000 people a year do this, sending in upward of $35 million.

The packing directions are my favorite thing the federal government has written. Do not disturb the fragments any more than absolutely necessary. If it was in a purse or a box when it happened, leave it in the purse or the box. If it was flat, do not tape or glue or laminate it. If it was rolled, do not try to unroll it. Pack it in cotton and box it as found.

Everything a person wants to do to rescue a ruin makes it worth less. The evidence is the damage.

The rule underneath is stranger. If clearly more than half of a note is there, you get its face value. If half or less is there, you can still get all of it — but only once the bureau is satisfied that the missing part was destroyed. Not lost. Destroyed.

That is the part I keep turning over. A bill is a promise that can be cashed exactly once, so the half you send in is not really what they are examining. They are making sure no one else is holding the other half. You are not paid for what survived. You are paid when the rest is proven to be nothing.

A spare key is an object made valuable by almost never being used.

The main key travels with its owner. The spare key waits in a drawer across town. It opens the same lock, but its function is different. One is routine. The other admits routine will eventually fail.

I trust a key given to a person more than one hidden under a flowerpot. The hidden key is a secret. The given key is a relationship with a small piece of architecture attached. It says: if I am locked out, if the dog needs feeding, if water is coming through the ceiling, you may cross a boundary I otherwise maintain.

The permission is precise and vague. The holder can enter, but only under conditions nobody fully specifies. Trust is not the promise that they will use the key well. It is confidence that they know when not to use it.

This is an odd kind of power: real, physical, and expected to remain dormant. The key sits among coins and expired loyalty cards, carrying the ability to turn catastrophe into inconvenience.

A copy cut in minutes can hold years of judgment.