In fact, the most interesting thing is that this pronunciation is basically universal in the whole country, which means that no matter which region or dialect, the word "one" is pronounced as "Yao", basically without exception. In China, where the span between north and south and east and west is so large, how can this pronunciation be unified throughout the country?
Call me if you need anything.
I don't know if you have noticed that the numbers read by soldiers in film and television dramas are all like this, and "1234567890" is read as "Yao 23456 is afraid of dogs". In fact, all this needs to be understood from our knowledge of point acoustics and phonetics.
In the early days, the soldiers in our revolutionary army came from all corners of the country, and it was inevitable that they all spoke with southern accents and could not understand each other. The pronunciation of "2" is the most confusing. As we all know, if comrades-in-arms don't speak English on the battlefield, it will basically cause serious consequences. Therefore, in order to solve this problem, the army leaders specially unified the pronunciation of these numbers, so that soldiers of different languages would not misunderstand in combat.
Another important reason is that both the numbers "7" and "1" have the sound "I". If two comrades-in-arms don't hear clearly during the battle, they are likely to make mistakes, and such mistakes are likely to be a matter of life and death. So, everyone came up with a way, that is, read "1" as "Yao" and "7" as "turn", so that there will be no more mistakes.
Because these appellations are very practical, after the founding of New China, these military appellations were transformed into civilian appellations, and over time, they were used to oral use by all of us. Now you understand.