References used when writing the HP-GL/2 (and HP-GL and PCL 5) driver include:

    "The HP-GL/2 and HP RTL Reference Guide", 3e (Addison-Wesley, 1997).
    	
    "HP LaserJet Programming", A. Binstock, B. P. Babcock, and M. Luse
    (Addison-Wesley, 1991).

    "The Product Comparison Guide for HP-GL/2 and HP RTL Peripherals", HP
    Manual Part No. 5959-9734.

    "The HP 7550A Interfacing and Programming Manual", HP Manual Part
    No. 07550-90001.  Second edition, 11/86.

    "The HP 7475A Interfacing and Programming Manual", HP Manual Part
    No. 07475-90001.  Fourth edition, 7/86.

    "Firmware Determines Plotter Personality", by L. W. Hennessee,
    A. K. Frankel, M. A. Overton, and R. B. Smith, Hewlett-Packard Journal,
    Nov. 1981, pp. 16-25.

    "Firmware Provides Simple and Powerful Plotter Operation",
    T. J. Halpenny, Hewlett-Packard Journal, April 1985, pp. 34-36.

    "PCL 5 Comparison Guide", HP Manual Part No. 5021-0329.

    "PCL 5 Printer Language Technical Reference Manual", HP Manual Part
    No. 5961-0509.

As of this writing, the last two manuals are only available from HP as part
of a larger `technical reference bundle' ("The PCL Documentation Package",
Part No. 5021-0330).
