This is a first draft of what is intended to be a complete inventory of options for civil timekeeping. Just compile the options now - we'll undoubtedly express our opinions about each later.
Speaking of which, newcomers may be unaware of the list archives at http://rom.usno.navy.mil/archives/leapsecs.html. There are a lot of creative ideas in there worth additional exploration. Two that jumped out at me last night are Mark Calabretta's daily epsilon corrections and Ed Davies' idea to issue a leap second whenever possible (i.e., leap 1s forward one month, 1s backward the next, whenever |DUT1| < 0.9s allows). What I like about the latter is that a synchronization step is therefore indicated by the ABSENCE of a leap second. What I like about the former is that it addresses the actual issue head-on - kind of refreshing actually. The value of such suggestions is not only that they could each be used to solve the problem in front of us (Davies' idea is valid under the current ITU standard!) - but that they also bring needed clarity to the analysis of the problem. Please remark on any gaps you see, especially missing categories: I) Existence A) adopt a civil time standard B) no civil time standard II) Multiplicity A) a single international civil time standard B) multiple civil time standards III) Locale A) restrict focus to Earth B) Solar system-wide solution IV) Synchronization A) Type 1) Solar 2) Atomic 3) Other (e.g., sidereal, lunar, dynamical, relativistic, ...) B) Overloading 1) None 2) Dual (e.g., UTC is synchronized to both Solar and Atomic scales) 3) Multiple (e.g., Earth+Mars+Atomic) C) Method 1) steps (I'm tired of the word "leap) a) arbitrary size b) fixed size i) second ii) minute iii) hour iv) other 2) rates ("rubber seconds") 3) both D) Triggering 1) manual (e.g., reset a clock by hand) 2) automatic E) Adjustment 1) discontinuity 2) time slice (e.g., UTS) F) Scheduling 1) as needed 2) fixed in advance G) Optimization 1) remain within tolerance (e.g., 0.9s) 2) minimize figure of merit (e.g., DUT1) H) Frequency 1) continuously 2) daily 3) monthly 4) annually 5) decade 6) century 7) greater than a century I) Notification 1) monthly 2) six months 3) annually 4) decade 5) fifty years 6) surprise I wouldn't be surprised if my biases are still evident. Please help me to remove these and to avoid adding any of your own. The structure is also too flat - categories might benefit from hierarchical nesting. Rob Seaman National Optical Astronomy Observatory
