Does give me an accurate mmr?

DeaftWarrior - Summoner Stats - League of Legends
DeaftWarrior / / Lv. 56
So I have been playing my placement games for solo/duo and check my estimated mmr on after every ranked game. I noticed that when i won 3 in a row it only gave me a +10 after ever won game and after i lost one it went down from silver 1 mmr to silver 4 mmr. I found this very strange and unfair and didnt really understand how it worked. I lost the next game, a Warwick game where I didnt do too well it went up from silver 4 to silver 2. How is this even possible and why does it do this? isnt it supposed to give a higher estimated rank when i win one and lose mmr when i lose a game?
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