Visitors pump air into a tank, and the pressure change is recorded on a video display. As the pressure increases, less air enters the tank with each pump. On the screen, the curve rises with the increasing pressure but begins to flatten our as it reaches a maximum. Visitors then release air from the tank, a little at a time. As the pressure decreases, less air leaves the tank each time. On the screen, the curve drops with the pressure decrease but begins to flatten as the tank empties. The curves show the mathematical pattern called an exponential decrease.