Simon Marlow wrote:

...

John suggested using (pico)seconds since 1970-01-01 00:00:10 TAI. Isn't this equivalent to saying that ClockTime is the number of seconds since 1970-01-01 00:00:00 UTC?

Yes.

TAI started ticking on 1 Jan 1958.

UTC started ticking on 1 Jan 1972, and started 10 seconds behind of TAI (to keep it within 0.9 sec of UT1).

So before 1 Jan 1972, UTC is defined as being the same as TAI? Or is it just undefined? Cheers, Simon