client-side system clock accuracy...

browser local time (locale): (missing time on client-side since beginning of 1972 = sec)
browser UTC time (ISO8601):UTC (arne's UTC minus browser's UTC: sec)
arne's UTC time (ISO8601):UTC
arne's TAI time (ISO8601):TAI (TAI minus UTC = blahsec)
arne's leap second counter:sec arne's server ping (round trip time): sec (#)