[Help - Other] ELO and How it Works

[Athenall]

Just a quick question on how ELO works.

Seems like when I log off then log back on the next day my ELO drops.

I've also noticed when I leave a game my ELO drops.

Do I need to afk in-game to keep my elo?
And, do i need to finish the entire match (all rounds) to stop my ELO dropping?

I tested it when I logged off last night; noting down my ELO. Then when I logged on today it had dropped.

I also went in-game, played 10 or some matches, noted my ELO and left then realised my ELO had dropped.