Bio-electrical Impedance-These are common in gyms or on body fat scales. Your body fat percentage is estimated by how long it takes a very small electrical charge to pass through your body. The electrical impulse travels faster through muscle than it does through fat. These are quick and convenient, but usually not as accurate since the charge may just arc through the upper or lower body and as a result may not give you a complete picture of your overall fat. Hydration levels can also skew the results.
Hydrostatic Weighing-This is an older method that uses Archimedes principles of water displacement. You will probably only find these at a University since they are so large and expensive. You sit in a dunking chair and blow all the air out of your lungs as you are slowly lowered into a small pool of water. You then have to hold still as long as you can. The water displacement is measured to help determine your body fat. It is a difficult process and uncomfortable for the test subject, but very accurate.
|Bod Pod machine|