Excerpt length

Now matter what I write in this column the exerpts does not change. And they are different for each post, and there are excerpts now matter how short a post is.
I have set the excerpt length to 55, and I tested it with a post that contained 3 words, then there ar two words in the excerpts, and I have to click read more to see the last word. I then edited the post to 4 words, and then there are 3 words in the excerpt.

In longer posts there is different amount of words, some have 55 other have fewer. There is nothing written in the excerpt boks in WP.