Well, isn't this something. Lots to consider (and I'm behind on all the comments atm.) I worked in aviation operations for a number of years (prior profession)

Well, isn't this something. Lots to consider (and I'm behind on all the comments atm.) I worked in aviation operations for a number of years (prior profession) and lived and breathed UTC. I wrote this then, so it's ... from last century. (Not in the wayback machine anywhere. I had to dig it back up.) >>>THE UNIVERSAL CLOCK : EXPLAINED by The AceyMan Most anyone who can read a language (as you are doing now) is familiar with 'time' and 'timekeeping'. This short essay hopes to explain the concept of non-local, or universal time, and promote its standardization. Until 1993, the clock that was set as a reference for all local time zones was kept in the United Kingdom. Due to its position at the Greenwich meridian, it was refered to as 'Greenwich Mean Time', or GMT. This clock was the world standard for all time zones, and never changes, ie, no savings time, no adjustments, except for accuracy. It is _defined_ as the world standard for time. So, when a nation or geographical area decides what local time is, they still must have a reference to set it against. (Time is relative, remember). GMT is that standard. For example, in the eastern United States, local (non-daylight) time is 5 hours behind GMT. That is to say, if GMT is 1800 hours (and yes, it uses a 24 hour, or 'military' clock), then US eastern time would be 1300 hours, ie, 1800-500=1300 or 1:00 pm. Now the confusion with local time occurs mainly when either of two things happens. First, when a person moves from time zone to timezone frequently and must make constant calculations to determine what time it 'really' is, or how long he's been awake, driving, burning fuel, running his computer, accruing hours, charging his customers, or any various other important numbers. This is frequent in transportation, especially aviation, where many time zones may be traversed in a short period. Second, when one is working with a worldwide communications system and may be talking with persons outside of your local timezone, sometimes FAR OUTSIDE your local time zone. In this case, GMT is especially useful, because by referring to GMT, one can still know what time that person is referring to, without asking where he is. For example, if you know what GMT is, and I know what GMT is, and I say, "I have to leave to go to a meeting at 1400 GMT", then the other person knows when that person will be leaving. S/he won’t have to ask "well, what's your local time now, so I can figure out how long it is before you go". GMT spares all parties from such time-consuming calculations. GMT should, and this author hopes WILL BE the clock for the world in the near future, as it should be. We owe the widespread use of global communications, particularly the Internet, for this expectation. ### I stand by most of that now (but I would do at least one rewrite says older me, heh). Doing time sums and differences on the fly across multiple time zones is loco. For both fuel and personnel planning. It's not just weather reports and ETD/ETA times. We are crunching time ALL time in air ops, and you have to have a pinned baseline. I think the time has long past to go unified. Then the only question you have to ask someone is "What's your UTC offset?" E.g., in your .plan file or S4B header text. Problem handled. /Acey [edit: unix errata]