Original version sent 2006 December 09 23:22:04 GMT+11:00, but did not make it to list. I have modified it (including the subject) slightly since then. I am not in favour of alphabetic abbreviations as designators of time zones or time offsets. First, their role is not well defined. Do they apply to A: a geographic region and its entire time-offset history and future, B: a particular single offset from UTC/GMT, or C: a particular set of two or more offsets from UTC/GMT and "rules" describing when changes from one of these offsets to another occur? Second, there seems to be no requirement for them to be globally or historically unique. I would support designators of the following kinds: O-1: a numeric specification of a single offset from UTC/GMT (e.g. "-04:00") Z-1: a specification applying to a point on the earth's surface and indicating the entire history (and expected future history) of the time kept at that point by nearby human beings, as in the tz database (as I understand it) Actually, I might also consent to: O-1A: a numeric specification of two (or more) offsets from UTC/GMT that apply periodically (e.g. "+10:00/+11:00"), though preferably only if such a specifier is unique in the context it is used in (+10:00/+11:00 applies both to Tasmania and mainland southeast Australia, but the two regions change from +10:00 to +11:00 at different times at present, so using that label for a time-specification offset as things currently stand would not be ideal unless it were clear from the context which changeover dates and times applied) and Z-1A: a specification applying to a well-defined, invariant region of the earth's surface and indicating the entire history (and expected future history) of the time kept by human beings occupying that region In the headings I've used to name these types of designator, the "O" indicates applicability to offsets and "Z" indicates primary applicability to zones. However, a Z (zone) designator could also be applied to an offset, in which case it means the offset that applies in that zone (which in the case of Z-1 is a point, not a region). Type O-1 is by far the easiest to work with, and perfectly adequate for many single-instant specifications. Only if (1) a period of time (including possibly a single date) or a repeating scheduled event is to be specified for a particular geographic location or (2) the offset that will apply is not yet known with adequate certainty, as it is tied to yet-to-be-finalised conventions for a particular place, might a single offset not be up to the task. (Have I missed any?) If it is judged that a zone designator for a time specification cannot be avoided, we have the problem of what time is applicable for the period (an hour in the majority of cases) after clocks are retarded, when times that have already passed in the zone are repeated. My only suggestion of what to do about this is to establish a convention that, in the absence of indication to the contrary, the second occurrence of the time specified should be assumed. There is also, of course, the related problem of what to do if a time is specified that never occurs in a zone, because it is skipped over when clocks are advanced. What else could be done besides taking such a specification to mean the instant of the changeover? If some apparent standard or official abbreviated designator is not clear, a lot of effort seems to be put into crafting a "suitable" one for the field labelled (for reasons that aren't all that clear to me) "FORMAT" in the tzdata files. I get the impression that people derive a sense of security from the authority and credibility supposedly lent to time specifications by such labels. Only it is a false sense of security, I would contend. These abbreviations seem to be seized upon by implementors of time-management software as though "official" and indispensable and to be used wherever plausible. I would like to see such enthusiasm diverted to the use, instead, of far less ambiguous and far more informative and helpful designators (like type O-1 especially). I might also add my vehement objection to using numbers derived from time offsets to label zones when the offset indicated by the number does not always apply. An example of this is "EST5EDT". Using offsets to label zones seems from my experience to be almost standard practice in time-related software, but it is grossly misleading when, as is very often the case, the indicated offset simply does not apply for part, indeed sometimes the majority, of the year. If numeric designators of such zones _must_ be used, then _both_ (or all, should there ever be more than two) offsets should be indicated (with equal emphasis). I would, as well, completely avoid the use of the term "standard" to distinguish one of two (or more) offsets that apply in a given zone. It may sometimes be a designation given by a relevant authority, but it is by no means always used, and it is a very poor choice for a generic designation of the less advanced of two offsets that apply at a particular location, since it is far from clear that a standard exists from which the offset that applies could be unambiguously inferred. I think any attempt at pinning down a particular offset as "standard" for a place or region based on longitude should be abandoned. Exceptions - cases of times being kept that deviate considerably from what one would expect (if it is clear at all) given the longitude - are not rare but abundant. Let me list some: the Aleutians, Alaska, Argentina, the Azores, Iceland, Madeira, the Canary Islands, Spain and France, peninsula Malaysia and Singapore, central Australia, parts of far-eastern Russia, the Chatham Islands, and, of course, though not true of the zone as a whole, western China. The term "standard" is applicable to whatever offset is being observed: it is the standard set by those (in authority) observing it (and their subjects). I suggest the terms "basis" and "advanced" instead as generic distinguishers of the two offsets that are periodically observed at any particular location (the latter applying to the offset that is "ahead"), though "winter" and "summer" are also not bad, except that "summer" cannot be unambiguously abbreviated to "S". "Advanced" and "Basis" have the pleasing property of having initials "A" and "B", "A" time being ahead of "B" time. Should more than two offsets ever annually apply to a zone, subsequent letters of the alphabet could be used to distinguish them. I hope I haven't strayed into territory outside the purview of this list.