The weight balance we use in lab have 3 levels of impedance. Bioelectrical impedance analysis is a method for estimating body composition and in particularly body fat. Commercial weight scales have usually only one level of impedance, 2 at best. So they can’t be as accurate than scales in lab. Furthermore, the variations of hydration’s levels can influence highly the results.
To minimize these inaccuracies, you need the following procedure: weight yourself the morning fasting and after urinating and having bowel movement.