A flat sheet beam is deflected across the anode which is partially covered by a parabolically stenciled screen "grid" that acts as the tube's output.[8] Parallel-output PCM tube, an analog-to-digital converter with per-bit, vertical anode bars with perforations encoding the Gray code.[9] A flat, horizontal sheet beam was then vertically deflected by the input analog signal across the perforated anode array, causing the digital representation of the analog signal to appear on the anodes.