How can I create a punctilio for verifying path width in Illustrator?

Spreadshirt design guidelines dictate that all lines and elements need to be a thickness of at least 1.5mm. They suggest you can verify this by:

using a 1.5mm dot (punctilio) to mouse over the thinnest parts of your design and 1.0mm circle to mouse over this space between the lines.

How can I achieve this in Illustrator CS6 Mac?