[LEAPSECS] Footnote about CCITT and UTC

[Tony Finch]

On Fri, 12 Dec 2008, Poul-Henning Kamp wrote:

>

> PS: According to Wikipedia, ISO 31-1 defines a day as 86400 seconds,

> anybody here who can verify if this is really the original text ?


ISO 8601-2004 cites ISO 31-1, and specifies several meanings for "day",
one of which is equivalent to 86400 seconds.

The ISO web site says that ISO 31 has been withdrawn and replaced by ISO
80000 (published in 2006). ISO 31-1 and -2 are replaced by ISO 80000-3.

quote from ISO 8601-2004 ...

2.2 Time units, nominal durations and time intervals

2.2.1 second

base unit of measurement of time in the International System of Units (SI)
as defined by the International Committee of Weights and Measures (CIPM,
i.e. Comite' International des Poids et Mesures)

NOTE 1 See also ISO 31-1.
NOTE 2 It is the base unit for expressing duration.

2.2.2 leap second

intentional time step of one second to adjust UTC to ensure appropriate
agreement with UT1, a time scale based on the rotation of the Earth
[Rec. ITU-R TF.460-5]

NOTE An inserted second is called positive leap second and an omitted
second is called negative leap second. A positive leap second is inserted
between [23:59:59Z] and [24:00:00Z] and can be represented as [23:59:60Z].
Negative leap seconds are achieved by the omission of [23:59:59Z].
Insertion or omission takes place as determined by IERS, normally on 30
June or 31 December, but if necessary on 31 March or 30 September.

2.2.3 minute

unit of time, equal to 60 seconds [ISO 31-1]

2.2.4 hour

unit of time, equal to 60 minutes [ISO 31-1]

2.2.5 day

unit of time unit of time, equal to 24 hours [ISO 31-1]

2.2.6 calendar day

time interval starting at midnight and ending at the next midnight, the
latter being also the starting instant of the next calendar day

NOTE 1 A calendar day is often also referred to as day.

NOTE 2 The duration of a calendar day is 24 hours; except if modified by:
-- the insertion or deletion of leap seconds, by decision of the
International Earth Rotation Service (IERS), or
-- the insertion or deletion of other time intervals, as may be prescribed
by local authorities to alter the time scale of local time.

2.2.7 day

duration duration of a calendar day

NOTE The term "day" applies also to the duration of any time interval
which starts at a certain time of day at a certain calendar day and ends
at the same time of day at the next calendar day.

Tony.
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