Warner Losh wrote: >The markers aren't the same. I was referring to the PPS marks in a time signal, and because TAI and UTC tick the same seconds the marks work equally well for both. Taking MSF as a specific example, the onset of each per-second carrier-suppressed interval (specifically, the instant when that point in the signal leaves the transmitter) occurs at the top of a second of UTC(NPL). UTC is always an integral number of seconds offset from TAI, and so by construction UTC(NPL) is always an integral number of seconds offset from TAI(NPL). Hence each of the marks also occurs at the top of a second of TAI(NPL).
>TAI doesn't actually exist until after the fact. Nor does UTC. >Could one create, in real time, a TAI signal, sure. But no one does. Taking MSF again as a specific example, it's just as much a TAI signal as it is a UTC signal. The PPS marks serve equally well for both, subject to the UTC(NPL)-UTC = TAI(NPL)-TAI realisation error. The time code transmitted alongside the marks doesn't directly encode either UTC or TAI, so decoding to either requires some out-of-band information. (The broken-down time that is directly encoded is in UTC plus the UK's current timezone offset, and nothing in the signal says what that offset is. There's a bit saying whether the offset includes DST, but there's nothing saying what the winter-time offset is. The signal format spec <http://www.npl.co.uk/upload/pdf/MSF_Time_Date_Code.pdf> is clear that a change to the UK's winter-time offset wouldn't be detectable from the post-change signal.) >So while an outside may see "oh! look! TAI is a nice way to label seconds that >doesn't suffer from the leap second issue, let's use it!" the insider reacts >to that suggestion >with horror because they know all the behind the scenes machinations. The same machinations also lie behind UTC. >So maybe I'm again off in the weeds trying to differentiate between philosophy >and a >notion of the right thing and politics and ideology. I'm open to there being philosophical differences, and of course taking UTC as a whole it certainly does have such differences from TAI. But (for the leap-seconds form of UTC) those differences are only in how the seconds are labelled. At the sub-second level, UTC incorporates TAI's features in their entirety, by reference. Identical behaviour, identical philosophy guiding that behaviour. -zefram _______________________________________________ LEAPSECS mailing list [email protected] https://pairlist6.pair.net/mailman/listinfo/leapsecs
