I send my photos for commercial development. I notice there are 5 digits which I suspect are the settings, but I am not sure. The shop I go to only vary the last digit and sometimes the second last digit as well. So the numbers usually appear as "N N N N 2". Sometimes it is N N N 1 2 and so on. Can someone please explain what these represent? I am not too happy with the colours of my photos, the shots I overexpose tend to come back really dark from the shop.