sub Checksum {
	my @Arguments = @_ ;
	my $Start = $Arguments[0] ;
	my $Size = $Arguments[1] ;
	my $FileName = $Arguments[2] ;
	
	my $FileHandle ;	
	unless ( sysopen $FileHandle, $FileName, 0 ) {
		die "\nsysopen failed";
	}
	
	my $BufferByte = 0 ;
	my $Checksum = 0 ;
	my $ChecksumLoopCounter = 0 ;
	my $ChecksumByteOffset = $Start ;
	unless ( sysseek($FileHandle, $Start, 0) == $Start ) {
		die "\nsysseek error" ;
	}
	while ( $ChecksumLoopCounter < $Size ) {
		unless ( sysread ( $FileHandle, $BufferByte, 1) == 1 ) {
			die "sysread size error" ;
		}
		my $Byte = ord($BufferByte);
		$Checksum = unpack("S" , pack("S", $Checksum + $Byte));
		$ChecksumLoopCounter++ ;
		$ChecksumByteOffset++ ;
	}
	close $FileHandle ;
	return $Checksum;
}