In Halo 3, are promotions decided by highest skill or current skill?

[James S]

If I get a skill level of 50, but it drops back down to the 40's, would I be promoted to general when I got 600 exp, or would I be stuck as a brigadier? and is it possible to be demoted once you ceach a skill-specific rank?

 

[benny]

it is decided by highest skill.
your rank will never drop down after you get to your highest level.

 

[Bob S]

your highest rank will stay even if you drop down. i am a 46 in doubles then dropped to a 44 but i am still and 46 overall. so when i get enough exp i will keep promoting as a brigadier.