GNOME Bugzilla – Bug 644682
"nanometer" not abbreviated to "nm", because "nm" used by "nautical mile"
Last modified: 2011-04-19 23:50:22 UTC
I guess a user is more likely to be using "nm" as "nanometer" than "nautical mile". Nautical miles can be abbreviated as "nmi" as indicated by http://en.wikipedia.org/wiki/Nautical_mile
This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.