Three officers were in charge of the company I served in. They were all First Lieutenants differing only in date of rank. So the senior 1st Lt. of the three was the commander, next was the executive officer, next was a platoon leader.
I got promoted to sergeant the same day as another soldier in our company who is 30 years younger than I am. Since we can't decide who is in charge on date of rank, we would use time in service if one of us had to be in charge.
Inside the Army, the rank on our chests is very significant. Outside--not so much. A few nights ago, my wife took our son to movie night at Wharton Elementary School. One of the other parents is full time in the Army National Guard. I had not met him until movie night. My wife introduced us saying, "This is Sergeant ________ that I told you so much about." He looked at me, smiled, shook my hand and said, "Captain ________ . . ." He was nice about it, but he definitely wanted me to know my wife had his rank wrong.
I have mentioned before that most of the people I work with in civilian life have not been in the military and have no immediate family members who are soldiers. For my wife and most of my coworkers sergeants, captains, colonels, and generals are all soldiers who are in charge of somebody. My coworkers know in a vague way that there is a rank structure, but it is much too arcane to bother with. And it would be completely useless to try explain the difference among the various ranks from sergeant through sergeant major or what the heck a warrant officer is--and why are they almost all chiefs?
I am in the same situation as a bicycle racer. In a good year I am a mid-pack racer for whom a top ten is a great day. But I am a racer which makes me different from a non-racer. So people who know as much about bike racing as I know about figure skating ask me if I am racing in the Tour de France or other professional bike racing events they have heard about. So for those who know nothing about racing, I could be Lance Armstrong's teammate. For those who know nothing abut the Army, General David Petraeus and I are the same age and both were in Iraq last year, so how much difference could there be?