Library /sys$common/syshlp/dbg$help.hlb DEBUG, Built in Symbols, %WIDTH  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Specifies the current width of the screen, in columns, as used by
    the debugger.

    For example, the following command defines a screen mode window
    named MIDDLE that occupies a region around the middle of the
    screen:

    DBG> SET WINDOW MIDDLE AT -
    _DBG> (%PAGE/4,%PAGE/2,%WIDTH/4,%WIDTH/2)