On 01/07/11 12:59, Clive D.W. Feather wrote:
Now imagine a second clock. This also ticks once per second. Right now it's 34 seconds behind the TAI clock, so it is saying 2011-07-01 11:28:11. This clock has 60 minutes to the hour, 24 hours to the day, 28/29/30/31 days to the month, and 12 months to the year, but while it usually has 60 seconds to the minute, it sometimes has 59 or 61 - these minutes are always the last minute of a month. So at the end of this year it could tick any of:
2011-12-31 23:59:56 2011-12-31 23:59:56 2011-12-31 23:59:56 2011-12-31 23:59:57 2011-12-31 23:59:57 2011-12-31 23:59:57 2011-12-31 23:59:58 2011-12-31 23:59:58 2011-12-31 23:59:58 2012-01-01 00:00:00 2011-12-31 23:59:59 2011-12-31 23:59:59 2012-01-01 00:00:01 2012-01-01 00:00:00 2011-12-31 23:59:60 2012-01-01 00:00:02 2012-01-01 00:00:01 2012-01-01 00:00:00 2012-01-01 00:00:03 2012-01-01 00:00:02 2012-01-01 00:00:01 2012-01-01 00:00:04 2012-01-01 00:00:03 2012-01-01 00:00:02
(and we don't yet know which of them it will be). This is the UTC clock. Note that TAI-UTC is always an integer number of seconds.
And even *that* goes horribly wrong after a couple of thousand years or so when we'd need more than one leap second per month! -- -=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@mev.co.uk> )=- -=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-