[tz] Why is `Etc/UCT` not an alias of `Etc/UTC`?

Paul Eggert eggert at cs.ucla.edu
Tue Mar 5 21:45:00 UTC 2019

On 3/5/19 12:00 PM, Isiah Meadows wrote:
> So basically just back-compat?

That's one reason it's there, yes.

My impression is that "UCT" is used on occasion as seen in the citations
below, although it's by far less common than "UTC". The question is
whether a shell command like "TZ=Etc/UCT date" should generate the
abbreviation "UCT" (perpetuating the "typo") or "UTC" ("correcting" it).
I am quoting the words "typo" and "correcting" so as not to prejudge the

Some sample uses of "UCT":

Gray JE, Machlan HE, Allan DW. The effect of humidity on commercial
cesium beam atomic clocks. Proc 42nd Ann Freq Control Symp 1988, 514-518.
https://dx.doi.org/10.1109/FREQ.1988.27649 "The implications of such
changes are quite significant in the generation of International Atomic
Time (TAI) and of Universal Coordinated Time (UCT)." The authors were
from the Time & Frequency Division, NIST.

Kouba J. Relativistic time transformations in GPS. GPS Solutions (2002)
5: 1. https://doi.org/10.1007/PL00012907 "It is interesting to note that
TT, TAI, and UTC (the Universal Coordinated Time) all have nominally the
same ..." The authorwas from the Geodetic Survey Division, Natural
Resources Canada.

Messerschmit DG. Relativistic Timekeeping, Motion, and Gravity in
Distributed Systems. Proc IEEE, vol. 105, no. 8, pp. 1511-1573, Aug.
2017. https://dx.doi.org/10.1109/JPROC.2017.2717980 "Universal
coordinated time (UTC) is the common civil definition of time." The
author is an emitus professor in the EECS dept, UC Berkeley.

Freeman RL. Standard time and frequency. Reference Manual for
Telecommunications Engineering, R. L. Freeman (Ed.) (2002).
https://doi.org/10.1002/0471208051.fre035 "Another necessity, in some
cases, is to be able to derive universal coordinated time (UCT) or a
comparable time scale." Freeman's a widely-published telecom author.

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