Ok ... I THINK I understand most of the concepts concerning supply. I mean, I know about the 0, 1/3, 2/3, 3/3 section of the screen for riverine & rail transport of supplies; I have a pretty good understanding of the importance of and manner of keeping my supply lines strong and open, etc.
What I would like to know, is what does he Supply Segment of a turn actually do/mean? The number after Supply Segment: varies ... sometimes 5, or less, sometimes 25, or more - and everything in between. What exactly does the number change mean?