Meatball landing system

Before technology was advanced enough to be able to calculate an aircrafts exact landing position, the meatball system was used. 

“Ball (or “meatball”; also known as “the source”) — indicates the relative position of the aircraft with reference to glide slope. If the aircraft is high, the ball will be above the datum lights; if the aircraft is low, the ball will be similarly below the datums. The further the aircraft is from the glide slope, the further the ball will be above or below the datum lights. If the aircraft gets dangerously low, the ball appears red. If the aircraft gets too high, the ball appears to go off the top”. -Wiki

Also, the Nasa logo is called the meatball because of this.