The .NUMBER CHAPTER command allows you to specify the number
    with which a sequence of chapters will begin. The next .CHAPTER
    command starts the sequence. Subsequent .CHAPTER commands will
    cause each chapter to be numbered one higher than the previous
    chapter. (See also .DISPLAY CHAPTER.)

    Format

      .NUMBER CHAPTER  [[+/-]n]

    Abreviated format

      .NMCH  [[+/-]n]

1  –  Parameters

 n

    The number that the next .CHAPTER will have. Entering the .NUMBER
    CHAPTER command without an argument gives Chapter 1.

 +n

    Adds n to the number of the most recently issued .CHAPTER. The
    result is the number that the next .CHAPTER will have.

 -n

    Subtracts n from the number of the most recently entered
    .CHAPTER. The result is the number that the next .CHAPTER will
    have.

2  –  Default

    Sequential decimal numbering, beginning with 1.