itions.html#picaspoints">picas</a>
down from the top of the page and begins the running text 3 picas
(the HEADER_GAP) beneath that, which means the effective top margin
of the running text is <nobr>7-1/2</nobr> picas (visually approx. 1
inch).  However, if you give mom a literal top margin (with
<a href="typesetting.html#t-margin">T_MARGIN</a>),
she ignores the HEADER_GAP and starts the running text at whatever
top margin you give.
</p>

<p>
Footers are treated similarly.  Mom sets footers 3 picas up from t