Each hub you write has a score which reflects the quality ,popularity,comments and uniqueness of that hub-also extra little efforts like photos or videos on the hub.This score will fluctuate initially,i.e. for a few days and then settle down.As readership falls off ,the score will also fall somewhat.It's unpredictable...but hubs with a score of 75 or above appear to have a better chance of being read.
The number on your pic is your hubber or author score-it goes up and down also,but once you have a few good hubs published you will have a better idea of what your average is.It can fluctuate too sudden drops or sudden rises-inexplicably-it appears some little 'machine' controls it:)-so don't worry too much if you wake up some morning and find you've dropped -5 or so.
The hubber score tends to be higher if you spend some time on the forums ......!
I hope this helps somewhat.