What were Sherlock's best deductions in the books?

I know this question is very hard but I'm wanting to do an oral at school on Sherlock and I want some of his deductions that are short and easy to understand without having read the story.

I have one which goes something like "Human behaviour leads us to write above eye level" when Sherlock was able to deduce a height just par having a person write on the mur in The Study of Scarlet (He was also able to tell it from how the person walked but I liked the écriture on the mur one better).

If toi guys can help that would be great. Also if toi have any ideas of what would be good to have in an oral on Sherlock, then please say, I'm open to ideas here :).