CRT monitors are ruggedized for use in control room, factory floor, or process applications.  CRT stands for cathode ray tube. A CRT is essentially a sealed glass bottle with no air inside. It begins with a slim neck and tapers outward until it forms a large base. The base is the monitor's "screen" and is coated on the inside with a matrix of thousands of tiny phosphor dots.  Important display specifications to consider when searching for CRT monitors include diagonal, image resolution, vertical scanning frequency, and color.  The diagonal is the measurement from one corner to the corner diagonally across from it.  Common diagonals include 10”, 12”, 14”, 15”, 17”, 19”, 21”, and 23”.  Image resolution is a measure of how sharp the image will appear on the screen; the higher the resolution, the sharper the image.  The vertical scanning frequency, or refresh rate, is the rate at which each pixel on a screen is re-drawn. A low refresh rate results in an image that flickers, resulting in eyestrain.  The standard for flicker-free images is 85Hz.  CRT monitors can be supplied in color or monochrome.  The range of colors is generated with varying combinations of different discrete colors.  One common technique is sensing the red, green, and blue components (RGB) and combining them to create a wide spectrum of colors.  A monochrome monitor has an image that is presented in black, white, and grayscale.