Body fat scales use a technique called Bioelectrical Impedance Analysis... or BIA for short.
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.
The amount of resistance to the electrical current relates to how much fat-free mass a person has and their body density.
Body fat scales don't actually measure your body fat percentage. They determine your body density.
Your body position, the amount of water in your body, your food intake, skin temperature and recent physical activity can all adversely affect the results of body fat scales.
To achieve accurate, consistent results, you must 'standardise' the way you perform each test. That simply means making each test with your scales as similar as possible.
1. Use them to measure your progress only. Don't compare your body fat percentage to tables or to your friends score.
2. Choose body fat scales that have the right profile for you. If your children are going to use them make sure they can be calibrated for children like the Tanita BC 543 Innerscan Family Body Composition Monitor. If you're an athlete (+10 hrs of strenuous exercise a week) the same thing applies. This is important. It makes a big difference.
3. Measure out some water one hour before you test yourself. Make sure you always drink the same amount of waterone hour before you test yourself.
4. Measure yourself at the same time of day for each test.
5. Your skin temperature affects the electrical current used by the scales. It's difficult but try to test yourself in a similar room temperature each time.
6. Don't test yourself after exercising. When you exercise you sweat and when you sweat you lose water. This affects your hydration levels and hence... the results.
7. Thoroughly clean the foot pads and then dry them off each time you test.
8. Buy the most expensive body fat scales you can afford. Accuracy will almost certainly increase with price. Try the new Tanita BC 545N Segmental Body Composition Monitor.