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<H2><A NAME="SECTION000467000000000000000">SLA_DTT - TT minus UTC</A>
<A NAME="xref_SLA_DTT"> </A><A NAME="SLA_DTT"> </A>
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<DL>
<DT><STRONG>ACTION:</STRONG>
<DD>Compute <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img19.gif"
ALT="$\Delta$">TT, the increment to be applied to
Coordinated Universal Time UTC to give
Terrestrial Time TT.
<P> <DT><STRONG>CALL:</STRONG>
<DD><TT>D = sla_DTT (DJU)</TT>
<P> </DL>
<P> <DL>
<DT><STRONG>GIVEN:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DJU</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>UTC date as a modified JD (JD-2400000.5)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>RETURNED:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>sla_DTT</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>TT-UTC in seconds</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>NOTES:</STRONG>
<DD><DL COMPACT>
<DT>1.
<DD>The UTC is specified to be a date rather than a time to indicate
that care needs to be taken not to specify an instant which lies
within a leap second. Though in most cases UTC can include the
fractional part, correct behaviour on the day of a leap second
can be guaranteed only up to the end of the second
<IMG WIDTH="82" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$23^{\rm h}\,59^{\rm m}\,59^{\rm s}$">. <DT>2.
<DD>Pre 1972 January 1 a fixed value of 10 + ET-TAI is returned.
<DT>3.
<DD>TT is one interpretation of the defunct timescale
<I>Ephemeris Time</I>, ET.
<DT>4.
<DD>See also the routine sla_DT, which roughly estimates ET-UT for
historical epochs.
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<ADDRESS>
<I>SLALIB --- Positional Astronomy Library<BR>Starlink User Note 67<BR>P. T. Wallace<BR>12 October 1999<BR>E-mail:ptw@star.rl.ac.uk</I>
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