DEC also offered an optional hard-copy device called an electrolytic copier, which fit into the blank panel on the right side of the display. This device was able to print, scan-line by scan-line, an exact replica of the screen onto a damp roll of special paper. It did this by electroplating metal from an electrode into the paper. The paper ran between two electrodes. The electrode on one side was a thin straight bar oriented across the paper width. The electrode on the other side was a thin helical bar wrapped around a rotating drum. One rotation of the drum scanned an intersecting area of the electrodes across the width of the paper. While the copier did an admirable job of capturing the contents of the screen, the output of the copier had an unfortunate resemblance to wet toilet tissue. Digital patented the innovation of having a single character generator provide the text font for both screen and copier.