A disclosed last-line overscan system and method allow for sampling of video display characteristics such as RGB cathode currents during each frame of displayed video for an underscanned video monitor without distortion of the visual display. Detection of the initiation of the vertical sync signal operates to overscan the last display line by driving the trace off the visual display area and away from the active raster. Sampling may then occur during an interval in which no visual display is possible thereby preventing distortion of visual information and preventing undesired brightness in the active raster. Subsequent to the interval for sampling of the RGB beam currents, vertical retrace is effectuated for display of the succeeding video frame. The video trace of the raster is bumped from the video display area and beyond the normal viewing area or escutcheon of the CRT screen during last-line overscan by providing a current surge for a preselected interval sufficient to allow for desired diagnostic sampling and testing, such as cathode current sampling.