n1,n2,...n6

    Indicate positioned numbers in a section header. The commas
    correspond to the dots in the printed section number. For
    example, to set the next .HEADER LEVEL to 3.5.2.4, you would
    enter the following commands:

       .NUMBER LEVEL 3,5,2,4
       .HEADER LEVEL

 +nN

    Adds n to the current value of the parameter N.

 -nN

    Subtracts n from the current value of the parameter N.