between 2 and 95 percent, and an altitude of . The printing paper was an diameter roll, and the paper tape was a roll of wide tape. Nylon fabric ink ribbons were wide by long, with plastic spools and eyelets to trigger reversal of the ribbon feed direction. Communications interface The communications module in the Model 33 was known as a Call Control Unit (CCU), and occupied the space to the right of the keyboard and printer. Various CCU types were available. Most operated on the telephone network and included the relevant user controls; variants included rotary, DTMF ("Touch-Tone"), and card dialing. An acoustic coupler for a then-standard telephone handset was also available. Another CCU type was called "Computer Control Private Line", which operated on a local 20 mA current loop, the standard serial protocol for computer terminals before the rise of RS-232 signaling. "Private Line" CCUs had a blank panel with no user controls or displays, since the terminal was semi-permanently hard-wired to the computer or other device at the far end of the communications line. Related machines The Model 32 line used the same mechanism and looked identical, except for having a three-row keyboard and, on the ASR version, a five-hole paper tape reader and punch, both appropriate for Baudot code. Teletype also introduced a more-expensive ASCII Model 35 (ASR-35) for heavy-duty use, whose printer mechanism was based on the older, rugged Model 28. The basic Model 35 was mounted in a light gray console that matched the width of the Model 33, while the Model 35 ASR, with eight-hole mechanical tape punch and reader, was installed in a console about twice as wide. The tape reader was mounted separately from the printer-punch mechanism on the left side of the console, and behind it was a tray for storing a manual, sheets of paper, or other miscellanea. To the right of the keyboard was a panel that could optionally house a rotary dial or Touch-Tone pushbuttons for dialing a connection to a network via telephone lines. The printer cover in later units also featured sound-deadening materials, making the Model 35 somewhat quieter than the Model 33 while printing and punching paper tapes. All versions of the Model 35 had a copy holder on the printer cover, making it more convenient for the operator when transcribing written material. Teletype Model 35 is mentioned as being used in "Experiment One",