Some of those BF scales can be way off. The college I graduated from has hydrostatic weighing and wanted to compare various other devices to this, which is the gold standard. The closest to underwater weighing is actually calipers with someone who is well trained in how to measure skin fold. The more measurements you take from various sites, the more accurate it becomes. However, if they are not well trained, it can vary by 3-6 points. When I tested, underwater showed 4.5%. Calipers showed 5%. The other electronic devices showed anywhere from 8-23%. The worst by far was the hand-held unit that has to electrodes on the handles. It never gave any measurements even close to UW or caliper.
Good luck with your work-outs.