The horizontal or line frequency indicates how many lines are displayed on a screen per second. It is a measure of the displayable screen resolution and is adapted to the resolution of the graphics card
. The horizontal frequency results from the multiplication of the number of lines and the refresh rate
. Thenon-visible part of the picture, i.e. the area of the vertical blanking interval
required for the beam return from the lower right edge of the screen to the upper left edge of the picture, must be included in this consideration. For example, the line frequency of television with 25 fields and 625 lines is 15.625 kHz.