Our Office of Sponsored Research and our institute business office really want us to know about this, because they have sent this message out several times. New preparation guidelines for NSF proposals go into effect tomorrow.
Only the following typefaces will be acceptable (note that Times New Roman is not among them): Arial or Helvetica for sans-serif fonts, Palatino or Georgia for serif fonts, or Computer Modern for LaTeX users. A Symbol font may be used for Greek letters and other special math characters (such fonts are obsolete on platforms that support Unicode character sets, which MacOS 10.4 does). Font size must be 10 points or larger. Type density is limited to 15 characters per inch and 6 lines per vertical inch.
One of the e-mails notes reports of shrinkage during the PDF conversion process, and therefore recommends a minimum of 11 point type.
The type density and line spacing are simple to do. In the PostScript era, one inch is 72 points. (Other definitions have been used: Donald Knuth, in The TeXbook, gives 72.27 points to the inch.) As long as you do not choose a condensed version of your font, the 15 characters per inch should take care of itself if you meet the 10 point requirement. Likewise, setting your interline spacing to at least 12 points (13 if you are worried about shrinkage) will take care of the 6 lines per inch requirement.