You would have know to how much accuracy you want to know. Estimates are about ball parking a number into some other idea about an easy way to understand what a number represents. 5,000 might be a good estimation for a distance that you're going to walk, if the exact distance is 5,004. You get a pretty good idea of how far , time wise, energy required ect ect.. when you say 5,000 So estimation is really about making the numbers easier to use and understand. Numbers are "abstract" they only represent ideas.
