Since DateAndTime comment is out of date (sic !) and current implementation seems not free of bug, here is an effort to summarize and understand the whole thing, let's call this a review. Please tell me where my interpretations are wrong. 1) The DateAndTime is stored internally as - a point in UTC time (julianDayNumber, seconds, nanos) - an offset from UTC (a Duration) denoting the local time zone 2) The ticks method returns the UTC part {julianDayNumber. seconds. nanos} 3) DateAndTime print themselves in local time using the offset 4) other methods (with some exceptions) return the local dateAndTime parts (year month day hours minutes seconds) Exceptions are: - secondsSinceMidnight (which should be renamed secondsSinceMidnightUTC IMO, even if the method is classified private) - julianDayNumberUTC as the name tells So far so good (but secondsSinceMidnight which is error prone) What I find strange: - #hash uses the offset... Why ??? d1 := DateAndTime now. d2 := d1 offset: d1 offset + 1 hours. { d1 = d2. d1 hash = d2 hash. } gives #(true false), a clue? - #< compares julianDayNumber (the UTC inst. var.) with otherDate julianDayNumber (with otherDate local offset) which seems wrong, it should better use julianDayNumberUTC or (normalized) ticks. - #= could be simplified and accelerated if using #hasEqualTicks: (if the ticks are correctly normalized though which would be the case since #ticks:offset: does, unfortunately #setJdn:seconds:nanos:offset: does not). Some senders of #setJdn:seconds:nanos:offset: don't normalize the day/seconds/nanos, though it should be their responsibility (DateAndTime todayAtMilliSeconds: xxx) (DateAndTime todayAtNanoSeconds: xxx), not counting year:month:day:hour:minute:second:nanoSecond:offset: which does not either (many senders...). Maybe we should better let the normalization responsibility to #setJdn:seconds:nanos:offset:. It remain to analyze the conversion protocol (asYear etc...) which seems to use the local time year, but I don't understand the whole Timespan thing right now (why DateAndTime now asYear starts now, and not on january 1st?). Nicolas