Amplitude-modulated time code WWVB

the example above encodes following:

day 66 (march 6) of 2008
for minute beginning @ 07:30:00 utc
dut1 −0.3 seconds (therefore, ut1 07:29:59.7)
dst not in effect today, nor coming effect
there no leap second scheduled, current year leap year

the table below shows in more detail, ex column being bits example above:

announcement bits

several bits of wwvb time code give warning of upcoming events.

bit 55, when set, indicates current year leap year , includes february 29. lets receiver translate day number month , day according gregorian calendar leap-year rules though time code not include century.

when leap second scheduled end of month, bit 56 set near beginning of month, , reset after leap second insertion.

the dst status bits indicate united states daylight saving time rules. bits updated daily during minute starting @ 00:00 utc. first dst bit, transmitted @ 57 seconds past minute, changes @ beginning of utc day dst comes effect or ends. other dst bit, @ second 58, changes 24 hours later (after dst change). therefore, if dst bits differ, dst changing @ 02:00 local time during current utc day. before next 02:00 local time after that, bits same.

each change in dst bits first received in mainland united states between 16:00 (pst) , 20:00 (edt), depending on local time zone , on whether dst begin or end. receiver in eastern time zone (utc−5) must therefore correctly receive dst changing indication within seven-hour period before dst begins, , 6 hours before dst ends, if change local time display @ correct time. receivers in central, mountain, , pacific time zones have one, two, , 3 more hours of advance notice, respectively.

it receiving clock apply change @ next 02:00 local time if notices bits differ. if receiving clock happens not receive update between 00:00 utc , 02:00 local time day of change, should apply dst change on next update after that.

an equivalent definition of dst status bits bit 57 set if dst in effect @ 24:00z, end of current utc day. bit 58 set if dst in effect @ 00:00z, beginning of current utc day.