I'd like to clarify which year should be compared in from/to fields for rules (and zone lines). It seems reasonable that the AT field determines which year is to be compared (wallclock, utc or standard) -- is that correct? To give specific example: Rule Test 1999 only - Jan 1 0:00 2:00 - Rule Test 2000 only - Jan 1 0:00 0:00 - These are both wallclock rules, and suppose they are used in a region that is GMT+5. Then at UTC 31-Dec-1999 17:00 the WC time will turn to midnight....is that the point at which the clocks would be adjusted? And if so, in the following example: Rule Test 1999 only - Jan 1 0:00 2:00u - Rule Test 2000 only - Jan 1 0:00 0:00u - would the clocks adjust at UTC time 1-Jan-2000?