I've just reviewed the tz database for the first time and want to complement all the contributors. My contribution has to do with time at the South Pole. Information is a bit dated (1999), but in her book Ice Bound: A Doctor's Incredible Battle for Survival at the South Pole, Dr. Jerri Nielsen relates that the South Pole Amundsen/Scott Station changes the time it observes based on the season (Summer or Winter). In the summer season, the station observes the same time standards as McMurdo Station (to make it easier to co-ordinate supply flights - Note: McMurdo, in turn, orients their clocks to their NZ supply bases in Christchurch). Once the station is closed to flights (temperatures drop below the point where jet fuel turns to gel), they switch their clocks to co-ordinate with the schedules of their administrative support team (US contractor) in Englewood, Colorado. They remain on that time until flights restart in the Antarctic Summer. As the dates vary with local climatic conditions, I'm not sure that it is possible to code a "prospective" algorithm. Also, time zone seems a bit irrelevant in a location which sees total darkness for six months of the year, the sun never gets more than 23.5 degrees above the horizon, and twilight lasts several weeks before sunrise and after sunset. (all are described in the book). BTW, Nielsen's book is fascinating, not just from the perspective of an individual battling cancer in a truly (i.e., no external access for nine months) isolated location, but also from her description of what life is like at the polar station. Living in cramped, cold quarters with several dozen people for nine months where water is strictly rationed because of the energy required to melt it reminds me of some of the descriptions I've read about the space stations and their UNIQUE fragrance. I read somewhere that the contractor the National Science Foundation uses was changed recently, so I am not sure whether they are continuing to follow this timezone practice. Which brings up the question, what time does the International Space Station run on (Houston, UTC?) and should it be included in the tz files? When Rutan and Yeager made their round-the-world-without-refueling flight, what time did they observe? What time do International flights which cross time zones observe? Inquiring minds want to know . . . ;-) Ken Levy