TITLE: Way to compare three numbers with an algorithm.
QUESTION [5 upvotes]: Say I have values
10,
3,
6
What would be a way of finding a subjective difference between them. Or in other words, how close they are to each-other. 
So if i had 
3, 2.5, 2.8; they would be close together in relation to one another.
3, 10, 10.5; would not be close together, despite two values being similar.

REPLY [2 votes]: I'm not completly sure if that is what you want, but, how about this?

Three positive numbers  $x<y<z$ are "near" if
  $$\frac{z-x}{y}$$
  is "small".