I use a BIA machine to spot trends in my body composition, but I agree that any individual measurement is highly unreliable and highly variable (which makes spotting trends difficult, but hey, it is easy
). As an example, my body fat measurement routinely varies by 2% or more from one day to the next-- at the same weight, measured at the same time of day, under the same conditions, etc., etc. So, I would not place any stock in an individual measurement and would not even rely on a range of measurements for an accurate portrayal of my actual body composition (although they might show a statistically relevant change in body composition if you were bored and wanted to play with numbers).