8601 also requires the use of the Gregorian calendar, which did not
exist prior to 1582, for all dates. It is easy to extrapolate back.

For time, the concept of time zones and radio time signals synchronized
between countries certainly existed before 1961. The prevalent time
standard was UT2, a form of rotational time smoothed for seasonal
variation, and high precision clocks were steered to match it. Until
1972, atomic clocks were steered to it, prior to leap seconds. Prior
to the introduction of atomic time, I think you could substitute that
with little loss of accuracy.

If you go back another century, there were no time zones, everyone kept
local solar time, and clocks weren't very good anyway. However there
are records of departure of local time from time on the prime meredian
that are part of the time zone record.

What are you trying to do exactly and what time records are you having
trouble relating to UTC?


--- In ISO8601@yahoogroups.com, "pqrc96" <pqrc96@...> wrote:
>
> All the parts of the standard that discuss Universal Time or time
zones
> specify that everything is based on Coordinated Universal Time (UTC).
> But UTC didn't exist before 1961, and didn't assume its present form,
> with an integer number of seconds difference between International
> Atomic Time (TAI) and UTC until 1972. So isn't it formally incorrect
to
> use the Z indicator or a time zone offset before 1961?
>
> For the relationship between TAI and UTC see
> http://hpiers.obspm.fr/eoppc/bul/bulc/UTC-TAI.history
>