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+      DOUBLE PRECISION FUNCTION sla_DTT (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 sla_DT, which roughly estimates ET-UT for
+*     historical epochs.
+*
+*  Called:  sla_DAT
+*
+*  P.T.Wallace   Starlink   6 December 1994
+*
+*  Copyright (C) 1995 Rutherford Appleton Laboratory
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION UTC
+
+      DOUBLE PRECISION sla_DAT
+
+
+      sla_DTT=32.184D0+sla_DAT(UTC)
+
+      END