This attribute specifies the difference between TAI
and UTC (i.e. the number of leap seconds) at the moment corresponding to the
Frame’ s
Epoch value.
The default value of AST__BAD causes the number of leap seconds to be determined from an internal
look-up table, which is kept up-to-date manually by the AST development team. Therefore it is only
necessary to assign a value to this attribute if the version of AST in use is so old that it does not
include all leap seconds that occurred prior to the time represented by the Frame
’ s Epoch
value.