Dunno, but assume you are the captain, laying in your bed and some comes in telling 'ship sighted' then you ask what ship? they answer it with for example a merchant.
Now next question you as is perhaps how far away ? the spotter gives your a value, lets say 'about 5 km' in front of us.
So, you always have a value to start with. If it is 5104 meters or about 5 km, your desicison making is the same.
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