[LEAPSECS] Crunching Bulletin B numbers (POSIX time)

[Rob Seaman]

On 21 Feb 11, at 1117, Tony Finch wrote:


>> But note I am assuming that you want to represent an absolute point in time (say, an astronomical event) rather than an event identified by the position of the hands on a clock.


Yes, these are the two distinct classes of use cases in civil timekeeping.  System engineering requirements derive from both.

On Feb 21, 2011, at 6:28 AM, Ian Batten wrote:


> I suspect that most people want the latter.  The interests of those that want the former need to be accommodated, but I suspect that the communities that need solar time, were that to become unhinged from civil time, are smaller in number than those that need civil time whatever it may represent.


Words like Tony's "assuming" and Ian's "suspect" indicate the lack of a coherently applied engineering process.  Ditto the casual toggling between what third parties are assumed to "want" versus what they are suspected of "needing".  Problems are defined through an iterative process of converting conjectures into requirements.  There are well-known best practices for doing so.  It is jejune to seek a solution before characterizing the problem it is meant to solve.  More to the point, there may be more than one solution.


> We're casually assuming that everyone understands GMT to be "sort of" UTC, and not defining our terms any more accurately than that...


Rather, it has heretofore been the case that UTC approximates GMT thus connecting our artificial timekeeping systems to the natural synodic day.  "Everyone understands" that day means synodic day - even if they don't know what synodic means.

It is not only the best way, but focusing first on characterizing the problem would be the quickest way to find a satisfactory solution.  It may also be the only way.

Rob