A glass master is created as an intermediate step in the CD manufacturing process. It is a glass plate about 240 mm in diameter and 6 mm thick, with an adhesively applied photoresist coating. Its manufacturing tolerances are extremely tight, and the finished glass master has a shelf life of only a few weeks before it must be used. A “cutting” machine uses a helium cadmium laser to photographically expose the data spiral onto the glass master disc, while another laser is used to maintain focus and tracking. The contents to be recorded onto the disc (including all required subcode information) are played in real time from a 1630 video machine (see PCM deck) or DDP (actually DDP can be run at higher speeds) tape machine, or a properly formatted CDR, via digital connection. The intensity of the laser is varied by a modulator (which is controlled by the digital audio data) to create the variations in the exposing signal representing the 1’s and 0’s making up the material. The glass master is then used in the manufacturing process as the template or mold to produce the inside metallic layer containing the data in a compact disc.