Robert Elz wrote:
It makes no sense (to me) at all to convert TAI into any kind of (currently used) calendar type measurements -
Fair enough.
Certainly I don't think it makes any rational sense to have different length "years" (regular years and leap years, with a bizarre rule about which years are which) in TAI - though it is certainly sensible to have a unit bigger than seconds in which to measure lengthy periods...
Vernor Vinge has a wonderful set of SF novels ("A Deepness in the Sky", etc.), set in the far future, in which they measure time in kiloseconds, megaseconds, etc. There's also this marvelous passage concerning legacy software: Via a million million circuitous threads of inheritance, many of the oldest programs still ran in the bowels of the Qeng Ho system. Take the Traders' method of timekeeping. The frame corrections were incredibly complex -- and down at the very bottom of it was a little program that ran a counter. Second by second, the Qeng Ho counted time from the instant that a human had first set foot on Old Earth's moon. But if you looked at it still more closely... the starting instant was actually about fifteen million seconds later, the 0-second of one of Humankind's first computer operating systems.
What we really need to do is recognise that there is not [...] just one definition (one unit) "a second" - there are two entirely different things we use commonly [...] One is the thing TAI uses [...] The other is 1/84600 of a day [...] where a day is defined according to the (varying) rotations of the earth, and hence the second is not a fixed length, but a variable one. That's the POSIX second (time_t) value [...]
I don't entirely disagree, and indeed bringing UT1 to bear is an attractive way of trying to rescue the benighted Posix definition, but time_t is certainly not defined that way now, and I'm not aware of anyone implementing it that way! time_t seconds really are UTC/TAI seconds (except, of course, when they're not). [But perhaps what you're saying is that redefining time_t as UT1 is part of "What we really need to do".]