Visible area refers to the actual application, the area of the screen that can be used to display the image. Because the size of CRT display is actually the size of its picture tube. The part that can be used to display an image can't reach this size at all. Because the frame of the picture tube takes up a part of the space. Generally speaking, the visual area of a 17-inch CRT display is about 15.8-16 inches. The visual area of a 15-inch display is only about 13.8 inches. But for LCD, The nominal size is basically the size of the visual area. The space occupied by the border is very small. The visual area of a 15-inch LCD is about 14.5 inches. That's why LCDs look larger than CRTs of the same size. So 15 inches is basically enough for LCDs.
