Supply originates from OKH or STAVKA. (Or the Tblisi HQ, if the card is played)
If using the default simple supply rules, supply (and replacements) flow from OKH/STAVKA directly to the unit, following a path of least movement points.
Supply movement is very cheap along the rail-line/road hexes. (Moving several hexes for the cost of a single AP).
Supply movement is fairly cheap along rail-lines. (1 AP/hex)
Along roads, it is 3AP per hex.
Over other terrain, it varies, depending on weather and type of terrain. Crossing rivers is very expensive ranging from 25-100 AP's depending on the size of river.
You gain bonus AP's if the supply line moves through a VP city.
If the cost in AP's from OKH/STAVKA is 100 AP's (or less), then your supply level is green, and you get 100% of the requested supplies.
If the cost in AP's is 100-150, then your supply level is yellow, and you get 75%.
If the cost in AP's is 150-200, then your supply level is blue, and you get 50%.
If the cost in AP's is 200-250, then your supply level is red, and you get 25%.
If it is more then 250 AP's then you are out of supply and get nothing.
If a unit moves/fights/rails...or was attacked, then it will lose readiness. Readiness is regained by spending supply. Units also hold up to 20 rounds of combat ammunition. This is shown under rounds as a number from 0 to 2 with .1 being one turn.
If you use the hardcore supply rule, then supply (and replacements) flow from OKH=>Army=>Corp=>Unit.
“My logisticians are a humorless lot … they know if my campaign fails, they are the first ones I will slay.” – Alexander the Great