Rolling Average Formula

I have a spread sheet that has three columns (Midnight, Day and Afternoon shifts). I enter each number each shift produced on that day in their corresponding cell. I need to keep a rolling 30 shift average. This is an overall average and is not shift specific. So for example, when I enter Midnight shifts production, the 30 shift average will give me the average for the past 30 shifts updated automatically up to the last shift that I have entered. Can anyone help me out? I have an example attached..