On Thu, Jan 4, 2018 at 9:48 AM, Tony Finch <dot@dotat.at> wrote:

Greg 'groggy' Lehey <grog@lemis.com> wrote:
>
> A thing that nobody has mentioned, and for which I can't find a
> reference easily: didn't System V have time zone offsets the wrong way
> round? I have some recollection from about 1988.

It's enshrined in POSIX but I believe it goes back earlier than that.
http://pubs.opengroup.org/onlinepubs/9699919799/functions/tzset.html

As I understand it, POSIX TZ offsets are the wrong way round because it
was more convenient to omit the sign on the TZ offsets, and because Unix
comes from America that meant no sign -> west, negative -> east.

There's also a time interval measurement convention from the high precision time keeping world that has negative offsets 'forwards' and positive offsets 'backwards' which this matches. It sure was confusing to me when I first encountered it when the time scientists were telling me the measurements were backwards...

Warner