Now take a ruler or tape measure, and measure the actual image you are viewing, measure diagonally, and you will see that the actual measurement is smaller than the monitors claimed size. For example, my 19 inch CRT monitor, measuring the actual image from the bottom left hand corner of the picture to the upper right hand corner is actually 17.25 inches, or in other words, only .25 inches larger than 17 inches, if the monitor measurement were the actual viewing screen this 19 inch monitor would only qualify as a 17 inch LCD monitor. This is where the LCD measurement comes in.
LCD monitors are measured by actual viewable area of the screen. They do not have a large rounded out tube beyond the screen, it is a flat panel of Liquid Crystals behind which are a series of tube lights that shine through the color crystals to illuminate