How did the salute come from? What are the rules?

Salute originated in England. It is said that the British navy used artillery more than 400 years ago. Before a warship enters the port of a friendly country, or meets a ship of a friendly country on the high seas, in order to show no hostility, all the shells in the cannon on board are released, and the coastal gunboat of the other side does the same in return. This practice has gradually become a courtesy to pay tribute to each other. Because the largest warship at that time was equipped with cannon 2 1, firing 2 1 became the highest etiquette. The number 2 1 may be because the ancient British thought that multiples of 7 were auspicious, and there was a superstition in the British navy that even numbers were unlucky. On the battlefield of the army, when the warring sides stop fighting to clean up their own casualties, they will also call on their comrades to fight again. This is also the origin of shooting or shooting to commemorate the fallen soldiers. The number of shots is equivalent to the warship level (the number of guns). 2 1 the highest, and the following times are 19, 17, 15, 13. The different levels are as follows: 2 1 ring greetings to the head of state or other people at the corresponding level; Call 19 to greet the person in charge of the government or other personnel at the same level; Call 17 to greet officials at the level of Deputy Prime Minister.