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.