SUBROUTINE  PLTUR (XA,X1,DX,X2,XB,YA,Y1,DY,Y2,YB,W,PL)

C     [UNIT RETICLE]
C     COVER THE PLOTTER PAGE WITH A NET OF FIDUCIAL MARKS INDICATING
C     UNIT INTERVALS OF DATA.
C     (XA,XB)  X-VALUES AT X-MARGINS
C     (X1,X2)  X-INTERVAL TO BE RETICLED
C     DX       X-DISTANCE BETWEEN CENTERS OF FIDUCIAL MARKS
C     (YA,YB)  Y-VALUES AT Y-MARGINS
C     (Y1,Y2)  Y-INTERVAL TO BE RETICLED
C     DY       Y-DISTANCE BETWEEN CENTERS OF FIDUCIAL MARKS
C     W        WIDTH OF FIDUCIAL MARK
C     PL       PEN MOVEMENT SUBROUTINE
C     DX AND DY MAY BE SIGNED OR MAY BE ABSOLUTE VALUES, LIKEWISE
C     THE X-, AND Y-INTERVALS MAY BE EITHER INCREASING OR DECREASING.
C     PLTUR ASSUMES THE UNIT SQUARE FOR ITS PAGE FORMAT, SO THAT
C     PL=PLTCA IS A SUITABLE ARGUMENT.
C     [05-JAN-75]

      EXTERNAL    PL

      EX(X)=XS*(X-XA)
      WY(Y)=YS*(Y-YA)

      XS=1.0/(XB-XA)
      YS=1.0/(YB-YA)
      D=SIGN(DX,XB-XA)
      E=SIGN(DY,YB-YA)
      S=SIGN(1.0,D)
      T=SIGN(1.0,E)
      S1=S*X1
      S2=S*X2
      T1=T*Y1
      X=X2
      Y=Y2
   10 CALL PLTFM (EX(X),WY(Y),W,PL)
      X=X-D
      IF (((S*X).GE.S1).AND.((S*X).LE.S2)) GO TO 10
      D=-D
      X=X-D
      Y=Y-E
      IF ((T*Y).GE.T1) GO TO 10
      RETURN

      END