When DV_DURATIONs are used in time histories, the
intended unit of recording, e.g. "mins", "s", "days" etc needs to
be known. However, this is not the case with DV_TIME, DV_DATE_TIME,
DV_DATE, since they are usually understood as points from an epoch
or origin. Durations used in time based recording commonly differ
in the primary unit they are recorded in.