Why Does Google Analytics UV Keep Decreasing?

I have a site that I am only doing white hat stuff on. Updating content twice a day or at minimum once a week. When I view the UV using Google Analytics the numbers keep adjusting. For example two days ago it said 479 but today it says 437?

I do not understand why though. I tried to do some research through BHW but I could not find anything. Can anyone help me out with some sort of insight?