Apple Color Monitors: Cause of Thin Horizontal Line(s)

Why do some Apple color monitors have a thin line or lines across the screen?
The CRT has a specially constructed aperture grill that improves its convergence and produces a sharp and clear image. The aperture grill is a grid of vertical wires located just behind the CRT screen. These CRTs require a horizontal stabilizing wire or wires to help support the aperture grill. The stabilizing wires, which are thinner than a human hair, dampen the vibration of the aperture grill wires. If the aperture grill wires were allowed to vibrate then the display quality would suffer, each time somebody tapped the display or bumped the table where the display is located.

Typically, displays with a viewing area of 15 inches or less have a single horizontal grid wire approximately one third from the bottom of the display image. Displays larger than 15 inches typically have two wires, each about one-quarter to one-third of the way from the top and bottom of the display image. Televisions may have up to three stabilizing wires, but because of the constantly changing images are rarely noticed.

These Apple products include a tron-style CRT:
Published Date: Feb 20, 2012