I was referring to why typed papers were traditionally
double spaced
between the lines.
(this seems to have moved to coff@, which I think I am not on)
Ah, the traditional reason for doubling the "leading" (not that
there's any actual chemical-element-Pb lead in typewriting) is
for copy-editing purposes.
I'm not sure if traditional typesetting drafts had increased
leading like this.
Chris