SUBROUTINE CHKCBA(BLOCK,SUM)
C
C	This subroutine computes a simple checksum for
C	a block of 256 words.
C
	INTEGER BLOCK(256),SUM			!
	CALL ERRSET(70,,.FALSE.,,.FALSE.)	!Ignore overflow.
	SUM=0					!
	DO 10 I=1,256				!Compute a checksum
	SUM=SUM+BLOCK(I)			!for 256 words.
10	CONTINUE				!
	CALL ERRSET(70,,.TRUE.,,.TRUE.)		!Recognize overflow.
	RETURN					!
	END