The tester uses the calipers to pinch(it doesn't hurt) the skin on 3 to 7 parts of your body. The caliper is a gauge that measures the thickness of the fat.
The parts pinched are usually:
abdomen
back of the arm
thigh
hip
back of shoulder
The caliper is not exact. The margin of error is 4 points either way. The tester might not pinch exactly in the right area, or may pinch too hard or too light. Get tested before your workout. After working out, your body pumps up which may make the calipers gauge you to be fatter.
Bioelectrical Impedence
A low voltage is passed through your body to determine bodyfat. The slower the signal the more fat you have. Fat slows down the signal. The signal travels quickly through muscle because muscle is made up of 70% water and water conducts electricity. Fat is only 5 to 13% water so it slows down the signal.
Dehydration can make the readings false because less water is in your system. Stay away from alcohol or caffeine for 24 hours because these substances help to dehydrate the body.
If you are overly fat or really lean this test may not produce good results.
Underwater weighing
This is the most accurate method of testing. You get into a tank of water on a scale. Here is the hard part, you have to blow all of the air out of your lungs and bend forward until you are completely submerged. Make sure to get all of the air out because any extra air makes you appear fatter. You wait about 5 seconds under water while your weight is taken.
Your underwater weight is figured out by a mathematical algorithm that determines your bodyfat. This test is based upon the premise that muscle sinks and fat floats. Muscle is denser than fat therefore it sinks. The margin of error on this test is 2 percent.
