Abstract: A television raster centering aid comprises means for blanking a horizontal scan line located at the center of the vertical deflection field. In an illustrative embodiment, an operational amplifier is used to indicate the presence of the deflection field center based on the polarity of the current in the vertical deflection windings. A gating circuit receives information from the operational amplifier and from a source of horizontal synchronizing pulses. The gating circuit then generates a signal which is used to blank a horizontal scan line located at the vertical deflection center. In one embodiment the raster centering aid is used in a yoke adjustment machine for blanking a scan line in a flat-field video display.