Many of the macros I write are incomplete in that they are vulnerable to errors
caused by invalid data entry. For example, entering any non-numeric character
in a field for a coordinate of a vertex will cause the macro to halt with an
error. Usually that is fine for personal use, but to better "bug proof" macros,
you can add code that will restrict the input to entries that are valid for the
intended use. This macro demonstrates a couple of different ways this can be
done. Screen shot