“Call the ball” “Roger, I have the ball.”
Visual Landing System for a US Navy Aircraft carrier. As the aviator approaches the flight deck, the aviator watches the light and puts the ball in the centre of the square mirror.
The goal is to keep the ball in line with the row of green lights on either side of the mirror. The typical exchange to an incoming naval aviator, a la Top Gun, “call the ball” which illuminates the lighting system followed by, “You have the ball…”
Very practical mechanical system for tracking progress around the trajectory of an in-bound plane in the middle of the ocean. This has many great (slightly obvious) parallel for the skills of landing projects and tracking things.