	PROGRAM NULFIT
C	FITS A STRAIGHT LINE OF TYPE Y = A.X TO (X,Y) DATA PAIRS
	REAL  A,B,SUMX,SUMXY,SUMXX,SLOPE,SUM,DIFF,ERROR2,ERROR
	INTEGER  I,J
	DIMENSION  X(200),Y(200)
	DATA  I,SUMX,SUMXY,SUMXX,SUM / 0,0.0,0.0,0.0,0.0 /
	OPEN (UNIT=7, FILE='iris.dat', STATUS='OLD')
10	READ (7,*,END=12) A, B
	 I = I + 1
	 X(I) = A
	 Y(I) = B
	 GOTO 10
12	DO 13 J=1,I
	 SUMX = SUMX + X(J)
	 SUMXY = SUMXY + (X(J)*Y(J))
	 SUMXX = SUMXX + (X(J)*X(J))
13	 CONTINUE
	SLOPE = SUMXY/SUMXX
	DO 14 J=1,I
	 SUM = SUM + ((Y(J) - (SLOPE*X(J)))**2)
14	 CONTINUE
	DIFF = SUMXX
	ERROR2 = SUM/DIFF
	ERROR = SQRT(ERROR2)
	WRITE (6,15) SLOPE, ERROR
15	FORMAT (1X,' A = ',F6.3,' +- ',F6.3)
	STOP
	END
