Small "blackboard" meaning

[put413]

At the top of the battle screen, there's a small blackboard to the left of the large one. At the top of this blackboard, there's a 0-1/3-2/3-3/3.
What are these fractions signifying?...My guess is that they mean you have either :
less than 1/3 of your maximum forces of (rail, river, sea) or
1/3 of your maximum
2/3 of your maximum
3/3 or at full capacity.
Am I right on my assumption?

[arsan]

Yes, that's it.
It also mean than between turns your supply will be able to use the riverine/train transport to push supplies around during the 1st supply segment (if you have 1/3), the first and second (if you have 2/3) etc..
Basically, the more supply capacity you left unused on the blackboard the farthest your supplies will be able to go if needed.
Check this wiki entry
http://ageod.nsen.ch/aacwwiki/Supply_network#Supply_distribution
Its much better explained there.
Cheers