John Hawkinson replies:
Time handling bugs typically appear in the interfaces between systems that make contradictory assumptions.
I think phk's point ("text book example") was that these problems were more likely to have been detected in a world where everyone's default timescale (UTC) was not subject to leap seconds -- rare events that may not come up in the course of normal testing unless special care is given.
I think PHK has demonstrated the ability (and willingness :-) to hold up his own end of an argument. Should we ever find ourselves at the same conference, I'll buy him a beer in anticipation of a rousing discussion. There are several issues confounded here. First, an untested assertion that eliminating leap seconds will simplify time handling. DUT1 looms large in astronomical software and one would have to be convinced that this is not an issue with other disciplines. Second, that UTC is indeed "everyone's default". It is (rather loosely) the current civil time standard, but I fail to see why this makes it a default choice for a precision timing application. "Civil measurement" in the USA still revolves around twelve inches to a foot, but SI units are the default for American scientists as is true elsewhere in the world. I won't belabor my assertion that mean solar time is the obvious civil time standard. But why do we expect that an X-ray spacecraft would of necessity adopt such a standard? Third, leap seconds are a mechanism to realize mean solar time in practice. The underlying issues are those of solar time, not how this is achieved. One can assert that leap seconds should cease, but the fundamental civil timing requirements will remain in force. Some other mechanism for synchronizing our clocks to our home planet must needs be identified. The acknowledgment of a contingent need for leap hours shows that the authors of the ITU proposal understand this. Fourth, the need for leap seconds is growing quadratically as the Earth continues to slow. We have no business making ad hoc policies based on the rarity of events that are becoming more frequent. The need for "leap hours" will grow just as rapidly - and much more dramatically. A solution that ignores real world constraints is no solution. Fifth, normal testing should involve special care - or what is its value? In short, leap hours are - well - dumb. A proposal that relies on their use, naive. Rob Seaman National Optical Astronomy Observatory