Integer. Returns 1 if it succeeds and -1 if an error occurs.

The default scale factor is 100.
Note, of_set_print_scale() does not affect the scale of the visible page in Excel. For that you should use of_set_zoom().
Note also that although it is valid to use both of_fit_to_pages() and of_set_print_scale() on the same worksheet only one of these options can be active at a time. The last method call made will set the active option.