The contest history graph shows the contests from contest 0 to latest contest without considering if we participated in that contest or not.
It is difficult to see the graph if we have started giving contests late, as most of it will be a straight line at 1500 level.
also if we have not given a contest, then there will be a straight representing no rating change, which creates a confusion like we have given a contest and there is no change in rating, or we didn't participated in that contest.

I think the graph should only show the contests which we participated in. then it will be much more easier to see our progress in contests.