How come the locale/cups.pot is 55.4 % translated?

Example:

msgid "accuracy-units.mm"
msgstr "Millimeters"
msgid "accuracy-units.nm"
msgstr "Nanometers"

I think this is incorrect use of the po format.
The source language (english) string should be in msgid and all msgstr should be empty in a pot file.
If translators needs to know "accuracy-units.mm" and "accuracy-units.nm" the info can be added like so:

#. [maybe some text here] accuracy-units.mm
msgid "Millimeters"
msgstr ""

#. [maybe some text here] accuracy-units.nm
msgid "Nanometers"
msgstr ""