It's an average made from offensive fire values, quality, health, etc.... it's a rough estimate of combat power, although not use per se...we'll give formulas later on..
isn't it more logical to give 2 figures = one is the actual combat strength and second is the max. combat strength. This is easy to screen corp and divisions without having to go into detail.
F.e. Longstreets corp has 3 divsisions =
Jones division 325/340
Hood division 125/380
Kemper division 350/750
this will immediately give you the overview - Jones is pretty fit - Hood has been badly mauled and is pretty weak - Kemper is still strong but has already lost a lot.
If Longstreet has to flee f.e. - he might choose to detach Jones division to delay upcoming Union forces, while Hood and Kemper try to make it to a safe harbour.