[math]\displaystyle{ \text{All Groups} }[/math] the gun groups and sub-groups defined in the following tables.
[math]\displaystyle{ C_{Group} }[/math] the accuracy modifier of the group, given in the following table.
When a ship has additional bonuses to a group compared to her type, this bonus is summed as a separate "Group"
[math]\displaystyle{ N_{Group} }[/math] the number of guns of a same group.
[math]\displaystyle{ M }[/math] the Marriage bonus of 0.6 when applicable, 1 else.
This bonus is applied in all cases, so penalties are reduced by 0.6, as well as bonuses.
For Iowa-class with the USN 16" Mk7 guns, M may be better, the observed bonu being [math]\displaystyle{ \text{ACC}_\text{bonus} = 6 \times \sqrt{N_{16inch Mk.7}} + 12 \times \sqrt{N_{16inch Mk.7 GFCS}} }[/math].
For BB only: if the base maximum HP (unmodified & before marriage) is superior to 92, set fit bonuses are set to 0.
Do note that speed modding ships (to Fast+) has been observed to worsen the penalties on certain ships.