ATSC A/85 is a guideline for using loudness measurement for audio as opposed to the traditional peak/RMS. The -24 +/- 2 number means that a loudness measurement of -24 LKFS should be the target. The peak level of -10 dBFs or -10 dBTP should be heeded as well.
With a tool like Avid's Pro Limiter, or the Waves WFM loudness meter (among many others), you can measure LKFS and dBTP easily.
If you don't have a loudness meter, you may want to look into a (somewhat) automated tool to gain change your mix into a loudness spec. Video Toolshed makes a very inexpensive tool where you feed in your mix file, set the specs, and it outputs an adjusted file to match the spec.