How do innerscan scales (that measure body fat %, etc.) work?

I am looking into buying a Tanita innerscan scale. Can anyone tell me how it can supposedly measure one's body fat %, body water %, muscle mass etc? And can you tell me if you know, how accurate that you think they are? http://www.tanita.com/InnerscanScales.shtml

Public Comments

1. i try to steer away from anything that measures my body fat, so I can not help you sorry!
2. How Body Fat Scales Work And Why It's Important Body fat scales use a technique called Bioelectrical Impedance Analysis... or BIA for short. Very simply... A small and completely harmless electrical current is passed through your body. The electrical current passes more quickly through fat free tissue like muscle than it does through fat or bone tissue. So... The amount of resistance to the electrical current relates to how much fat-free mass a person has and their body density. Here's the first challenge... Like all body fat tests, body fat scales don't actually measure your body fat percentage. They determine your body density. The examiner (or the scales) then uses a formula to calculate body fat percentage based on body density. Bioelectrical Impedance Bioelectrical impedance methods are basically special body fat scales or hand-held devices that send a safe electrical signal measuring its return through the body. The signal will travel faster with water and since muscle is 70% water and fat contains little water, the body fat scale is able to make a distinction, plug the information into an algorithm and give you a reasonable body fat percentage estimate. Bioelectrical impedance is simple and quick. The scales are not outrageously expensive, usually $60 to $200, which makes it a practical method. Tanita makes some good ones. The consistency of these measurements is a bit questionable however. Changes in water retention, food intake, skin temperatures and minor posture changes among other things can affect the readings given by these devices. These variables can leave you with some perplexing numbers. While the bioelectrical impedance methods won't be as reliable as skinfold measurements methods, they are better than not getting a number at all. So if you're not a very patient person (and learning to get consistent body fat percentages with skinfold measurements will require a little practice and patience), body fat scales can provide serviceable body fat calculations. They will give you something to go on. For best results, try to keep all factors as close to identical each time you jump on your body fat scales (temp, posture, etc.).