A unit starts as an empty box but can be filled with Subformation.
HQ units keep track of transfer capacity points for land, sea and rail.
Supply points are kept track of on a unit level. Keep in mind if there is more supply points then troops that auto-carry it or transport-carry it the unit will move at speed of supply.
An air unit can have a setting at which readiness level and lower it will no longer intercept.
A unit can have a setting specifying at which percentage of losses (forced retreats and kills) it will start an orderly retreat.
A unit can have a setting specifying the percentage of the supply it ideally likes to receive next turn. Basicly it will allow you to get a unit to go on substenance and no longer gain/recover readiness , but not lose anymore either due to complete lack of supply.
A unit can have a setting specifying if it will or will not use its Anti Supply points. Disabling it can be a smart move to hide the presence of your units, since anti supply kills will give the enemy your presence away (or very close to it).
In the start of your turn each unit consumes supply. See Readiness Increase. If not minimum supply was present to keep readiness at least on same level, this statistic will be set somewhere below 100%. It gives hefty penalties in combat.
A HQ can have its color bar set.
A HQ can have its reserve supply setting defined.