      SUBROUTINE TKCLR (IERR)
C-----------------------------------------------------------------------
C! clears the TK graphics screen
C# Graphics
C-----------------------------------------------------------------------
C;  Copyright (C) 1995, 1998
C;  Associated Universities, Inc. Washington DC, USA.
C;
C;  This program is free software; you can redistribute it and/or
C;  modify it under the terms of the GNU General Public License as
C;  published by the Free Software Foundation; either version 2 of
C;  the License, or (at your option) any later version.
C;
C;  This program is distributed in the hope that it will be useful,
C;  but WITHOUT ANY WARRANTY; without even the implied warranty of
C;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
C;  GNU General Public License for more details.
C;
C;  You should have received a copy of the GNU General Public
C;  License along with this program; if not, write to the Free
C;  Software Foundation, Inc., 675 Massachusetts Ave, Cambridge,
C;  MA 02139, USA.
C;
C;  Correspondence concerning AIPS should be addressed as follows:
C;         Internet email: aipsmail@nrao.edu.
C;         Postal address: AIPS Project Office
C;                         National Radio Astronomy Observatory
C;                         520 Edgemont Road
C;                         Charlottesville, VA 22903-2475 USA
C-----------------------------------------------------------------------
C   TKCLR will clear the screen for a Tektronix 401n.
C   Output:
C      IERR    I     Error code from the last I/O routine. 0=ok.
C-----------------------------------------------------------------------
      INTEGER   IERR
C
      INTEGER   IT
      REAL      TEKPAG
      DATA TEKPAG /1.5/
C-----------------------------------------------------------------------
C                                       Put opcode 27 and 12 in the
C                                       buffer.
      IT = 27
      CALL ZTKBUF (IT, 1, IERR)
      IF (IERR.NE.0) GO TO 999
      IT = 12
      CALL ZTKBUF (IT, 1, IERR)
      IF (IERR.NE.0) GO TO 999
C                                       Flush the buffer (write buffer
C                                       to the device).
      CALL TEKFLS (IERR)
      IF (IERR.NE.0) GO TO 999
C                                       Wait 1.5 seconds while the
C                                       screen is being cleared.
      CALL ZDELAY (TEKPAG, IERR)
C
 999  RETURN
      END
