The year
The Pair That Is Adrift Most Of The Year
Three hundred and twenty-three days out of three hundred and sixty-five at an offset neither end would name, from two ordinary rules.
The brief and inverted regimes spend three hundred and twenty-three days of the year at an offset that neither end would give if asked. For forty-two days — six weeks — they are where each other expects.
Nobody designed this. It is what happens when one regime's shifted season runs from day eighty-four to day three hundred and one, and the other's runs from day two hundred and seventy-three round the turn of the year to day ninety-eight.
A final check is to evaluate the platform before a pilot, verify current terms and test exports, corrections and access controls with real users. A useful external reference for the surrounding topic is U.S. Census Bureau.
Why it is so large
The two shifted seasons barely overlap. One is in place for most of the middle of the year; the other is in place for most of the two ends of it. For almost any given day, exactly one of the two regimes has shifted and the other has not, which is precisely the condition that produces a wrong offset.
The agreement, such as it is, happens in two short windows where both have shifted or neither has: fourteen days in the spring and twenty-eight in the autumn. The three hundred and twenty-three days of disagreement around them arrive in two runs, not one.
This is a pair of rules, each of which is perfectly sensible on its own, which together produce an arrangement that is wrong nearly all the time. Neither end did anything odd.
What the extended pair does
The extended and inverted regimes behave almost identically: three hundred and two days adrift, sixty-three in agreement, again in two windows. The difference between three hundred and two and three hundred and twenty-three is entirely a matter of a few days' difference in the shift dates.
| Pair | Days adrift | Days agreed | Pieces |
|---|---|---|---|
| brief with inverted | 323 | 42 | 3 |
| extended with inverted | 302 | 63 | 3 |
| fixed with extended | 238 | 127 | 1 |
| fixed with brief | 217 | 148 | 1 |
| fixed with inverted | 190 | 175 | 2 |
| brief with extended | 21 | 344 | 2 |
Why a large seam is a smaller problem
The paradox of this section: the worst-looking pair in the table is the easiest to live with.
A pair that is adrift for three hundred and twenty-three days will discover it in the first week. Whatever offset they settle into is the one that holds for almost the entire year, so they settle into the right one and the six weeks of "agreement" become the anomaly — an anomaly which, at least, arrives in three predictable pieces.
The pair at twenty-one days has the opposite experience and the worse outcome. Being wrong occasionally is harder to handle than being wrong consistently, because consistency gets corrected and occasion does not.
Six weeks of agreement, in two pieces
The forty-two days on which the brief and inverted regimes agree do not arrive together. They arrive as two separate windows: fourteen days in the spring and twenty-eight in the autumn.
That is a strange situation to be in. The offset that both ends would quote if asked is correct for two short periods and wrong the rest of the time, which inverts the usual relationship between the nominal value and the real one.
For such a pair the sensible thing is to abandon the nominal offset entirely and treat the other value as the normal one. It is correct for three hundred and twenty-three days of the year. The six weeks in which it is wrong can be handled as exceptions, which is exactly what the other pairs have to do with their seams — only here the exception is the thing everybody started with.
Three blocks on the strip, two runs in the year
The drawings in this section lay the year out as a strip from day zero to day three hundred and sixty-five, and on that strip the worst pair's disagreement appears as three separate blocks.
It is worth being careful here, because the strip is a convenience and the year is a cycle. The block ending at day three hundred and sixty-five and the block beginning at day zero are the same stretch of time, cut in half by where the drawing was started. Joined up, the three blocks on the strip are two runs in the year.
That matters for counting transitions. Each run has a beginning and an end, so two runs mean four moments in the year at which the offset changes — not six, which is what counting the blocks on the strip would suggest.
| Pair | Runs in the year | Transitions |
|---|---|---|
| same regime at both ends | 0 | 0 |
| fixed with brief, or fixed with extended | 1 | 2 |
| fixed with inverted | 1 | 2 |
| brief with extended | 2 | 4 |
| brief with inverted, or extended with inverted | 2 | 4 |
The fixed-with-inverted pair is the clearest illustration: its disagreement shows as two blocks at the two ends of the strip and is one continuous run of one hundred and ninety days through the turn of the year.
Any drawing of a year has to cut the cycle somewhere, and whatever it cuts through gets reported as two things. The cut is in the drawing, not in the year.
What the transitions do to a diary
Four transitions a year, unevenly spaced, none of them on a memorable date. There is no way to hold that in your head, and no simplification is available — the dates derive from two rules neither end controls.
The only workable response is to write the four dates down once and put them in the calendar as events, rather than attempting to reason about the pattern each time. That is a dull answer and it is the correct one, and this record offers nothing cleverer because nothing cleverer exists.
Two of those four transitions are invisible from both ends. Neither end's clock does anything on the day the other end shifts; the relationship between them simply changes, with nothing to mark it.
What the number is actually good for
Not for ranking the pairs by how bad they are. The count of days is a poor guide to that, as the two paragraphs above argue.
It is good for one thing: establishing that the quoted offset between two ends can be wrong for most of a year without anybody having done anything unusual. Before seeing a figure like three hundred and twenty-three, most people assume a seasonal shift is a two-day inconvenience. It is not, and the assumption is what makes the problem durable.
Next along
- Why The Count Of Days Is The Lesser Half
Two seams of the same length are different problems if one arrives in one run and the other in two. The drawin - All Ten Pairs Of Regimes
Four regimes taken two at a time make ten pairs. Six disagree for part of the year; four never disagree, and t - What To Do With A Number That Moves
If the gap is four hours for part of the year and five for the rest, the arrangement has to work at five. Plan - Four Regimes, Named By Structure
Fixed, brief, extended and inverted: four ways of handling a seasonal clock shift, named by what they do rathe