How do I accurately check my body fat?

The human body has 60,000 miles of blood vessels. It has nerve impulses that travel to and from the brain at speeds of up to 250 miles per hour (faster than a Formula 1 racecar). It has 7000,000,000,000,000,000,000,000,000 (7 octillion) atoms yet when we stand on a weighing scales, none of this seems to matter.