On Thu, Sep 09, 2021 at 02:15:24AM +0000, Thaddeus H. Black wrote:

    .  nr SN (2 * \\n[SSS_SN_ORIG])

Alternatives include this:

    .  nr SN ((5 * \\n[SSS_SN_ORIG]) / 3)

Compared to the (2 *), the ((5 *) / 3) shifts the subsubsection
header 1.0en leftward:

    ABC(7)                 Linux Programmer's Manual                 ABC(7)

    SECTION FOO
           Foo flargh.

       Subsection bar
           Bar blargh.

         Subsubsection baz
           Baz mnargh.

    Linux                          1970-01-01                        ABC(7)

Whether the shift improves the visual is a question of taste, although
logically, the (2 *) is more consistent than the ((5 *) / 3) is.
The ((5 *) / 3) is depicted above.  The (2 *) is depicted in the earlier
email.  I have no preference.