NONUMBERLINES causes each line in the output listing to have the next sequential line number. However, because of macros or .incld files, the line number may not reflect the actual position in the source file. While this is useful for a cross-reference table, it may not be for other purposes. NUMBERLINES causes each source line to have the same line number as its position in the file. In this case, lines from macro expansions or .incld files do not have line numbers.