How Age of Sail ratings counted guns

Labels such as 74 and 80 describe ships by their total number of guns. The approximate bands given here put first rates at 100 guns or more and second rates around 90 guns, or roughly 86 upwards. Third rates run from 84 down to roughly 64 guns. The rating uses gun count as a shorthand for a ship's armament. The comparison with World War II asks why that shorthand lost its value as weapons became more powerful and served different purposes.