the larger the maximum value, the lesser the accuracy.

ie if you use a weight that can weight 100T, then the min it can weight will be like 50kg, so if you use that to weight a human, you will get 0, 50, 100 or 150 kg, even its 75kg, it can only tell you 50 or 100. i think all weight are about the same, it has a spring, and you press on the spring, then it go through a multiplier(or a tune) to give human a reading, if you use a super huge powerful spring, then you can weight extremely heavy thing, but cannot give you accurate reading if you measure something light.

so the best is know what you are going to weight, have a rough idea how much it will weight, and get a weighing scale that can do about 50% more(my preference), if you go kiasu, and get something that can weight 10 or 100x more, then your result will be less and less accurate.