I describe alignment to my players this way
Your alignment is like a dartboard. Good on the right. Evil on the left. Lawful on top. Chaotic on the bottom. The direction from center is your alignment and the distance from center is the intensity of your beliefs. That point on the board that describes what you believe and how you try to act becomes your target. (your professed alignment)
Every action is a dart tossed at the board. If you are steadfast and true to your beliefs the the most of the darts will be on target
It would not be unusual to every once in a while do something out of character and those actions appear on the board nowhere near your target but elsewhere depending on how the dm views them.
The importance of the action and the moral repercussions of it determine how far from the center the dart appears…
So say I profess to be lawful good… so my target is the 18/4 divider… I do my job, I pay my taxes, I don’t speed, I give to charity etc… Nothing special but I’m a nice guy who in general behaves himself. So my dartboard would have a cluster of darts around the 18/4 not far from center. There may be some a little high, a little left, a little low but in general the pattern shows I am who I claim to be a LG nobody.
Then I lose my job, my wife leaves me, and my mom dies. I get drunk one night and get in a bar fight and accidentally kill someone. So now I still have that LG cluster but I have a few darts on the other side of board including one opposite and pretty far out there.
Do I run, hide what I did, avoid the consequences and get more darts on the chaotic side. Do I hurt more people trying to get away and start accumulating darts below the bulls-eye.
Or do I turn myself in. Express real remorse and take full responsibility. Do my best to make restitution and serve my sentence. And accumulated darts that are not only on the LG quarter of the board but significantly further out than the boring nice guy who did what he should.
So at anytime you should be able to look at this dartboard and see a pattern of behavior. That is your actual alignment.
We went through a phase where we tracked alignment very carefully and each DM had a sheet of six dartboards labeled with character names and at least once session they’d put a dot on the board regarding the players actions. No one I know still uses the system that way exactly but its still how I see it in my head.
The one thing it doesn’t cover is the strength of conviction of those who are true neutral.