On Thu 2006/01/12 10:19:05 -0000, David Malone wrote in a message to: LEAPSECS@ROM.USNO.NAVY.MIL
>The reason that I came to this conclusion is because none of the >documents I've read say that UTC can be expressed as a real number >- they all suggest it is expressed as labelled seconds. (For example, >see the way that Rec. 460-4 gives UTC values - I've never seen an >official looking document that tries to write UTC as a real.) I have two time scales, TAI and UT1, that tick at very slightly different rates. I want to make TAI the basis for civil time keeping but I need to make adjustments occasionally to keep it in step with UT1. How do I do it? The answer provided by CCIR was to represent TAI in a variable-radix notation that matches (or appears to match), to within 0.9s, that of UT1 expressed in the usual calendar/clock format. This is done by varying the radix of the seconds field in a pseudo-sexagesimal clock format from 60 to 61 (or in principle 59) on occasions announced 6 months in advance. So if asked for a definition I would say that "UTC (post 1972) is a representation of TAI such that ... (you know the rest)". The point is that UTC is simply a representation of TAI. "Writing UTC as a real" reveals it to be TAI. Mark Calabretta ATNF