Minute
Non-SI unit accepted for use with the SI · quantity: time
Clocks went without a minute hand for three hundred years. The first tower mechanisms struck only the hours, and nobody minded: there was nothing in daily life that had to be measured more finely.
01 · Definition
A minute is a non-SI unit of time equal to sixty seconds. The second is defined through the frequency of a transition in the caesium atom; the minute is defined simply through the second, with no physics of its own: it is a pure convention about what counts as a convenient portion.
Sixty came down to us from the scribes of Babylon, and it stuck because of its divisors: sixty divides by two, three, four, five, six, ten, twelve, fifteen, twenty and thirty. An hour can be split into three equal parts only in this system — in a decimal one the result is a recurring fraction. That is precisely why attempts to move time onto a decimal count failed where the other metric reforms won.
The minute has a peculiarity no other unit has: it comes in different lengths. When a leap second is inserted into the scale of Coordinated Universal Time, the last minute of the day runs to sixty-one seconds. That has happened twenty-seven times since 1972, and in 2035 the insertions will stop — not because the Earth has begun to turn more evenly, but because that extra second costs digital systems more than the drift from the planet’s rotation does.
Prefixes are not applied to the minute: there is no such thing as a millininute or a kilominute. For shorter intervals one moves to the second with its prefixes, for longer ones to the hour and the day. This sets the minute apart from units like the bar or the electronvolt, which take prefixes readily.
The dial is divided not into sixty parts but into as many as you set. The crimson sector is the duration of the event; the yellow marks are the divisions of the hour. Watch how one and the same event takes on different notations, and which divisions give round numbers.
Twenty minutes is exactly a third of an hour, and that is the single reason the sexagesimal count outlived the metric reform. A third of a hundred is 33.33…, and a timetable cannot be built on a recurring fraction.
02 · Conversion
Enter a value — the sheet will convert it
The minute converts into seconds, hours and days exactly, by definition. The only inexact figures are the comparisons with the Earth’s rotation: a sidereal minute is 0.164 seconds shorter than ours, and over a day that adds up to almost four minutes.
The decimal minute of 1795 stands on a line of its own — 86.4 seconds. It existed lawfully in France for seventeen months.
Twenty-seven times since 1972 the last minute of the day has run to sixty-one seconds. An insertion is announced six months ahead, and each time it still brings down part of the servers: in 2012 the extra second halted airline reservation systems and several large websites. From 2035 insertions will be abolished, and the divergence from the Earth’s rotation will be allowed to accumulate — days will fall behind the scale, and that is judged the lesser evil.
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03 · Orders of magnitude
logarithmic scale: from a flash to a millennium04 · Measuring instruments
What minutes are counted with
An instrument for a single portion: turn it over and the minute is running. At sea the hourglass struck the half-hour bells, and its accuracy depended on the dryness of the sand — in damp weather the glass ran slow.
Huygens, 1656: the daily error falls from a quarter of an hour to ten seconds, and the minute hand acquires meaning for the first time. The second hand appears later still, when the accuracy of the escapement has caught up with it.
A second hand that starts and stops: the minute ceased to be a segment on the dial and became a measurable interval. That is what turned it into an instrument of sport, of medicine and of the factory floor.
It does not count the minute as such: it reproduces the second, and the minute follows by multiplying by sixty. The drift of a fountain standard is about a second in three hundred million years, so the minute inherits an accuracy nobody has any use for in daily life.
05 · Writing rules
Takes no prefixes, needs no full stop
The symbol is written as three lower-case Latin letters with no full stop. Between the number and the symbol there is a space, and a non-breaking one, so that the value does not get torn across a line break.
In technical texts eighty minutes may be written as a single number if what is meant is a duration rather than a clock reading. On a clock face the same amount must be written as 1 h 20 min.
06 · Neighbouring units
The minute stands between the second and the hour and is tied to both by a factor of sixty each way. The same word in geometry means a sixtieth of a degree — and the two scales are relatives, not namesakes.
Sexagesimal division applies to time and to angle alike — and that is no coincidence: both scales came out of Babylonian astronomy, where the sky was measured in the same units as the calendar.
07 · Historical section
How the sixtieth part reached the dial
Ptolemy divides the degree and the hour into sixty parts, following the Babylonian tables. The Latin translation, “the first diminished part”, gives the word minuta, and the second division gives secunda — that is where our second comes from.
Jost Bürgi builds a clock with a minute hand for the astronomer Tycho Brahe — to commission, not for a town. For another hundred years the minute hand stays an instrument of the observatory rather than a piece of everyday furniture.
A decree introduces a day of ten hours of a hundred minutes each: the minute becomes 86.4 seconds. Clockmakers issue dials with two rings, decimal and ordinary, and the public keeps reading the ordinary one.
The scale of Coordinated Universal Time is granted the right to insert a second so as not to drift away from the Earth’s rotation. That is how a minute of sixty-one seconds came into being — the only unit whose length is not fixed once and for all.
The one quantity where the decimal reform lost
The metric system moved length, mass, area and even angle onto base ten — the grad, with a hundred divisions to the quadrant, is still used in surveying. Time alone held out, and the reason is arithmetical: an hour of a hundred minutes cannot be divided into three, and a third of an hour is the commonest portion in any schedule.
Metrologically the minute is derived from the second and has no standard of its own. Yet it is the only unit in the series whose duration is not fixed: with a leap second inserted, the last minute of the day is sixty-one seconds long, and this is a lawful value, not an error of measurement.
Catalogue · units of measurement
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Seven SI base units, twenty-two derived ones with names of their own, and the non-SI units neither engineering nor daily life can do without. Each has a sheet of its own: definition, conversion, instruments, writing rules, history. In 36 languages.