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+      REAL FUNCTION sla_RVEROT (PHI, RA, DA, ST)
+*+
+*     - - - - - - -
+*      R V E R O T
+*     - - - - - - -
+*
+*  Velocity component in a given direction due to Earth rotation
+*  (single precision)
+*
+*  Given:
+*     PHI     real    latitude of observing station (geodetic)
+*     RA,DA   real    apparent RA,DEC
+*     ST      real    local apparent sidereal time
+*
+*  PHI, RA, DEC and ST are all in radians.
+*
+*  Result:
+*     Component of Earth rotation in direction RA,DA (km/s)
+*
+*  Sign convention:
+*     The result is +ve when the observatory is receding from the
+*     given point on the sky.
+*
+*  Accuracy:
+*     The simple algorithm used assumes a spherical Earth, of
+*     a radius chosen to give results accurate to about 0.0005 km/s
+*     for observing stations at typical latitudes and heights.  For
+*     applications requiring greater precision, use the routine
+*     sla_PVOBS.
+*
+*  P.T.Wallace   Starlink   20 July 1994
+*
+*  Copyright (C) 1995 Rutherford Appleton Laboratory
+*-
+
+      IMPLICIT NONE
+
+      REAL PHI,RA,DA,ST
+
+*  Nominal mean sidereal speed of Earth equator in km/s (the actual
+*  value is about 0.4651)
+      REAL ESPEED
+      PARAMETER (ESPEED=0.4655)
+
+
+      sla_RVEROT=ESPEED*COS(PHI)*SIN(ST-RA)*COS(DA)
+
+      END