The user may define subclasses of this class.
type: refers to whether Greenwich (UTC), GPS, or a local reference (e.g. a system clock) is being used to define the basis of time values. Note that because of leap seconds, UTC time is not continuous. The structure of time in the context of the Global Positioning System is identical to Universal Coordinated Time (UTC), but no leap seconds are introduced (beginning in January, 1980. Consequently, time with reference to the GPS system is continuous, but at variance with UTC.
offset: provides the difference in hours and minutes from Greenwich, regardless of whether type equals utc, gps, or local.
likelyTimeError: provides a non-statistical estimate of time error. Uncertainty with respect to a date and/or time may be defined by supplying a value for likelyTimeError. True time is assumed to be time interval.