of typesetting, a galley proof might be printed in order for proofreading to be performed, either to correct errors in the original, or to make sure that the typesetter had copied the manuscript properly, and correctly interpreted the markup. The final layout would be constructed in a "form" or "forme" using pieces of wood or metal ("furniture") to space out the text and images as desired, a frame known as a chase, and objects which lock down the frame known as quoins. This process is called imposition, and potentially includes arranging multiple pages to be printed on the same sheet of paper which will later be folded and possibly trimmed. An "imposition proof" (essentially a short run of the press) might be created to check the final placement. The invention of hot metal typesetting in 1884 sped up the typesetting process by allowing workers to produce slugs—entire lines of text—using a keyboard. The slugs were the result of molten metal being poured into molds temporarily assembled by the typesetting machine. The layout process remained the same as with cold metal type, however: assembly into physical galleys. Paste-up era Offset lithography allows the bright and dark areas of an image (at first captured on film) to control ink placement on the printing press. This means that if a single copy of the page can be created on paper and photographed, then any number of copies could be printed. The type could be set with a typewriter, or to achieve professional results comparable to letterpress, a specialized typesetting machine. The IBM Selectric Composer, for example, could produce type of different size, different fonts (including proportional fonts), and with text justification. With photoengraving and halftone, physical photographs could be transferred into print directly, rather than relying on hand-made engravings. The layout process then became the task of creating the paste up, so named because rubber cement or another adhesive would be used to physically paste images and columns of text onto a rigid sheet of paper. Completed pages become known as camera-ready, "mechanical" or "mechanical art". Phototypesetting was invented in 1945; after keyboard input, characters were shot one-by-one onto a photographic negative, which could then be sent to the print shop directly, or shot onto photographic paper for paste-up. These machines became increasingly sophisticated, with computer-driven models able to store text on magnetic tape. Computer-aided publishing As the graphics capabilities of computers matured,