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+      REAL FUNCTION slRVER (PHI, RA, DA, ST)
+*+
+*     - - - - - - -
+*      R V E R
+*     - - - - - - -
+*
+*  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
+*     slPVOB.
+*
+*  P.T.Wallace   Starlink   20 July 1994
+*
+*  Copyright (C) 1995 Rutherford Appleton Laboratory
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the
+*    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+*    Boston, MA  02110-1301  USA
+*
+*  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+*-
+
+      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)
+
+
+      slRVER=ESPEED*COS(PHI)*SIN(ST-RA)*COS(DA)
+
+      END