ambiguous instructions

So, I'm preparing a large document.  There are instructions for the layout.  One reads:

All margins (top, bottom, left, right) should be at least 15 mm (not including any footers or headers).

Hmm. Does it mean that, when measuring the margins, do not include any headers and footers in that measurement (that is, measure from the edge to the main text), or, when measuring the margins, do not include any headers and footers in the margins (that is, measure from the edge to the top of header/bottom of footer)?

Instructions are always unambiguous when you write them, because you know what you mean, so don't even see the alternative interpretation.  They become ambiguous only when someone else reads them. Sigh.