Actually those scales are useless. They use impulses to determine round trip calculations. So, if you drank a lot of water one day, and the next not a lot you will get 2 distinctive readings.
VBM, to lose that much body fat in 1 week, you would need to start at a higher BF%.
We did a grp weight loss program here at work. We used %BF as the base reading. So you could actually gain weight but your BF go down. I believe that it was for 8 weeks. I was using xfit at the time and in that 8 weeks, i went from 21% to 19%.
Even now, using a split between xfit and simplefit, 2 on 1 off, i went from 21% to 19% and that is with doing the zone diet and its been a little over a month.
Obviously your milage is going to vary, but to go from 22% to 17% i find it extremely hard to believe. Keving hit it on the head. waist at the navel minus wrist size. there is a chart to use so if you want post that number and your weight and i can tell you what it comes to.