SUBROUTINE GET_SYS ( NPAR )
C
C  This subroutine determines the system calibration error.
C  The calibration error is added to the error in the calibrated
C  visibility of each scan and it is adjusted until the chi square
C  is equal to the number of degrees of freedom.
C
C   NPAR  is the number of parameters in the combined fit.
C
C   SYS_CAL is the systematic error.
C
C     3 JAN 1991  David Mozurkewich
C
      IMPLICIT UNDEFINED (A-Z)
      SAVE
      REAL *4 PI, RAD
      PARAMETER ( PI = 3.1415926535 )
      PARAMETER ( RAD= 180. / PI )
      INCLUDE 'VPLOT.INC'
      INTEGER *4 ICHAN, I, J, MASK(4), IBASE, NDATA, NPAR(ichan)
      REAL *4 YDATA(NFIT), ERROR(NFIT), CHISQ
      REAL *4 CRMS, CMEAN, DELTA, GRID_SIZE, DOF
      LOGICAL CAL_SCAN
C-----------------------------------------------------------------------
      DATA MASK / 1, 2, 4, 8 /
C-----------------------------------------------------------------------
      DO ICHAN = 1, 4
          IBASE = BLIST(1)
          NDATA = 0
          CMEAN = 0.
          CRMS  = 0.
          CHISQ = 0.
          DO 450 I = 1, ISCAN
              IF ( IAND(OKSCAN(I),MASK(ICHAN)) .NE. 0 ) GO TO 450
              IF ( IAND(   BAD(I),MASK(ICHAN)) .NE. 0 ) GO TO 450
              IF (   BASE(I) .NE. IBASE   ) GO TO 450
              CAL_SCAN = .FALSE.
              DO J = 1, NCALSTAR
                  IF ( STAR(I) .EQ. CALSTAR(J) ) CAL_SCAN = .TRUE.
              END DO
              IF ( CAL_SCAN ) THEN
                  NDATA = NDATA + 1
                  YDATA(NDATA) = VCAL(I,ICHAN) / VEST(I,ICHAN)
                  ERROR(NDATA) = VSIG(I,ICHAN) / SCAL(I,ICHAN)
     $                         / VEST(I,ICHAN)
                  CMEAN = CMEAN + YDATA(NDATA)
                  CRMS  = CRMS  + YDATA(NDATA)*YDATA(NDATA)
                  DELTA = (YDATA(NDATA)-ERROR(NDATA)) / ERROR(NDATA)
                  CHISQ = CHISQ + DELTA * DELTA
              END IF
  450     CONTINUE
          IF ( NDATA .GT. 5 ) THEN
              CMEAN = CMEAN / FLOAT(NDATA)
              CRMS  = SQRT( CRMS/FLOAT(NDATA) - CMEAN*CMEAN )
          ELSE
              WRITE(6,*) ' ERROR NOT ENOUGH CALIBRATION SCANS '
              SYS_CAL(ICHAN) = 0.
              GO TO 900
          END IF
          SYS_CAL(ICHAN) = CRMS / 2.0
          GRID_SIZE      = CRMS / 2.0
          DOF = NDATA - NPAR(ICHAN)
          DO I = 1, 10
              CHISQ = 0.
              DO J = 1, NDATA
                  DELTA = (YDATA(J)-1.) / (ERROR(J)+SYS_CAL(ICHAN) )
                  CHISQ = CHISQ + DELTA * DELTA
              END DO
              GRID_SIZE = GRID_SIZE / 2.0
              IF ( CHISQ .GT. DOF ) THEN
                  SYS_CAL(ICHAN) = SYS_CAL(ICHAN) + GRID_SIZE
              ELSE
                  SYS_CAL(ICHAN) = SYS_CAL(ICHAN) - GRID_SIZE
              END IF
          END DO
  900     CONTINUE
      END DO
      RETURN
      END