Also called "refresh rate," vertical scan frequency is the number of times a CRT was redrawn per second. Measured in Hertz, CRTs ranged from 56 to over 100 Hz, but at least 70 was recommended to help prevent eyestrain. Only the latest model CRTs could support their highest resolution along with a high refresh rate.LCD Screens Do Not Refresh Static ImagesVertical scan frequency is not an issue with LCD displays because they do not use phosphors that have to be continuously energized. However, the data from the GPU's frame buffer is continuously sent to the LCD panel. Thus, all flat panels have a maximum refresh rate. Contrast with horizontal scan frequency. See interlace.