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Re: [sdw] intervalDuring can really compare the values of two date time stamps

From: Chris Little via GitHub <sysbot+gh@w3.org>
Date: Thu, 19 Jul 2018 13:49:15 +0000
To: public-sdwig@w3.org
Message-ID: <issue_comment.created-406282581-1532008154-sysbot+gh@w3.org>
Timestamps, such as defined in IETF RFC 3339 [https://tools.ietf.org/html/rfc3339 ] which is based on ISO 8601, can be compared and 'before', 'after', 'same time', 'during', 'overlapping', etc can be correctly established.

However, in general, two timestamps cannot be subtracted to give a duration, unless the calendars are precisely known and correctly implemented.

Please note that some implementations that look like timestamps, such as Posix or Unix seconds since the 1970-01-01T00:00:00.000Z epoch are not well behaved, as they do not always have a strictly monotonic sequence of increasing times. For example, to cope with leap seconds, Posix implementations reset the clock to the previous second. If the clock count is more frequent than every second, the clock times 'jump backwards' in this case, rather than pause and 'mark time'.

Does this answer your question?

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