The year

The Gap People Quote And The Gap They Have

A nominal offset is the number two ends tell each other. For six of the ten regime pairs it is wrong for part of every year.

When two ends describe the distance between them, they quote a single number. That number is a nominal offset: the difference between the two clocks at some moment, usually the moment somebody first worked it out, treated thereafter as a property of the arrangement.

For four of the ten regime pairs in this record, the nominal offset is correct every day of the year. For the other six it is wrong for somewhere between twenty-one and three hundred and twenty-three days.

A distributed team may look through the current settings, assign one pilot owner and review useful findings and false signals together. A useful external reference for the surrounding topic is Mozilla.

How long the quoted gap is wrong

plain: the pair is at its nominal offset
hatched: it is not

Four pairs drawn. The worst of them spends 238 days of the year at an offset that is not the one either end would quote.

Four of the six disagreeing pairs. The plain stretches are the days on which the number both ends quote is the number they have.

Computed from the two regimes. The shift dates are the record's own, chosen so that they differ; no place's rule is named.

The two ways it goes wrong

One end shifts and the other does not. The gap widens or narrows by an hour and stays there for the whole of the shifted season. The pair whose regimes are fixed and extended spend two hundred and thirty-eight days of the year in this condition — well over half.

Both ends shift, on different dates. For most of the year the gap is as quoted, because both have moved. Between one end's shift and the other's, it is not. The pair whose regimes are brief and extended spend twenty-one days a year like this: two weeks in spring and one in autumn.

Pair of regimes	Days the quoted gap is wrong
brief with extended	21
fixed with inverted	190
fixed with brief	217
fixed with extended	238
extended with inverted	302
brief with inverted	323

Four further pairs — each regime against itself — are never wrong, because two ends following the same rule move together.

The nominal offset is not a measurement. It is a measurement from one particular day, promoted to a permanent fact, and nothing tells either end when the promotion stopped being warranted.

Why nobody notices

Both of these failures are invisible from inside. Each end's clock says what it has always said. Each end's working day starts when it always starts. Nothing on either screen announces that the relationship between them has moved by an hour.

The discovery happens when somebody joins a meeting an hour early or an hour late, which is treated as a personal error and dealt with by apologising, rather than as evidence that the shared assumption has expired.

It then recurs, because the assumption has not been corrected — only the one meeting has.

What the hour actually does

An hour of unexpected offset is not a scheduling inconvenience. It is a change to the arrangement's capacity, and the size of the change depends entirely on where the arrangement was sitting.

A pair at a nominal gap of one hour, drifting to two, go from seven shared hours to six. Nobody notices and nothing needs to change.

A pair at a nominal gap of seven, drifting to eight, go from one shared hour to none. For those weeks or months the arrangement has no simultaneous time at all, and the daily meeting that was the whole point of it does not exist.

Nominal gap	Shared	Drifted to	Shared
1	7	2	6
4	4	5	3
7	1	8	none

The closer an arrangement sits to the edge, the more an hour of drift costs, and arrangements near the edge are exactly the ones that were carefully built around a single protected hour.

Why the drift goes unexamined even after it bites

Because the symptom is a person, not a system.

What the arrangement observes is that somebody did not turn up, or turned up an hour late, or scheduled something for an hour that turned out not to work. Every one of those reads as an individual error, and individual errors are dealt with by mentioning it and moving on.

Nothing in the symptom points at the calendar. There is no moment at which somebody says "the gap between us has changed", because nobody's clock changed in a way they noticed — each end's clock did exactly what their own rule said it would.

The diagnosis requires somebody to hold both rules in mind simultaneously and compare them, which is a thing nobody does unless they already suspect the answer.

A fault whose symptom is somebody's lateness will be treated as lateness, indefinitely, by reasonable people acting on the evidence in front of them.

What an honest statement looks like

Instead of "we are four hours apart", something closer to: "we are four hours apart for most of the year and five hours apart for about seven months of it", which is what a fixed-and-extended pair actually have.

That is an uglier sentence and it is the true one. Anybody planning a recurring commitment against the first version will have it land in the wrong hour for most of the year.

The practical rule

The gap to plan against is not the one quoted. It is the worst gap that occurs at any point in the year, because that is the gap the arrangement has to survive. If a pair at a nominal four hours spends part of the year at five, the question is whether the arrangement works at five — and if it does not, it does not work.