I only know about the Water tank which is the most accurate. You place your body in it, and weights are added I think. Somehow some measurements are gathered to get your body fat weight. Online calculators exist, as well as electronic waves that are sent int your body, the echo is recorded and analyzed.
The SI unit of length or distance is the meter.
Answer:
Parallel circuits are used in homes because the loads can be operated independently of each other. That means that you can have an electrical item turned on and running without needing to have all of the other loads on and running as well.