As for measuring with calipers: Google it.
When it comes to losing .8 lbs over a week, note that your body weight fluctuates greatly during the day due to water retention. (mine fluctuates about 5 lbs between morning and evening)
I notice that even with calipers, my bodyfat measurements fluctuate with the water weight about 1%.
As long as you are doing everything right, counting EVERY calorie, and not cheating (or at least, taking any cheats into account), don't worry too much about it. Pay attention to your diet. A little cheating can blow away hours of cardio.