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+.help dtt Jun99 "Slalib Package"
+.nf
+
+      DOUBLE PRECISION FUNCTION slDTT (UTC)
+
+     - - - -
+      D T T
+     - - - -
+
+  Increment to be applied to Coordinated Universal Time UTC to give
+  Terrestrial Time TT (formerly Ephemeris Time ET)
+
+  (double precision)
+
+  Given:
+     UTC      d      UTC date as a modified JD (JD-2400000.5)
+
+  Result:  TT-UTC in seconds
+
+  Notes:
+
+  1  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 only be guaranteed up to the end of the second 23:59:59.
+
+  2  Pre 1972 January 1 a fixed value of 10 + ET-TAI is returned.
+
+  3  See also the routine slDT, which roughly estimates ET-UT for
+     historical epochs.
+
+  Called:  slDAT
+
+  P.T.Wallace   Starlink   6 December 1994
+
+  Copyright (C) 1995 Rutherford Appleton Laboratory
+  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+
+.fi
+.endhelp