The reasoning behind using the pound is, if you are using fractions per say to get a side by side ration when you are doing 16 ounces to 1 pound you would want to have a unit rate.
750 ounces 16 ounces
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x pounds 1 pound
Do you see how much easier it is to convert from ounces to pounds when you have a unit rate? Now once you see how many times you had to multiply 16 to get 750 you can easily multiply that number by 1!
Because logarithms were a lot less time-consuming than other methods of finding roots. They were also more accurate in the sense that it was harder to make a mistake.
