A short script that will inject on any animelist on MyAnimeList scores that are scaled from 0 to 10. It means that if your lowest score is 5, it will become 0. It also calculate some values that you may find interesting and put it in variables. To use it, just paste this in your chrome console when you are on an anime list.

script.js

var n = document.querySelectorAll(".animetitle");
var arr = [];
var min = null;
var max = null;
var total = 0;
var count = 0;
var noteCount = {};

for (var i = n.length - 1; i >= 0; i--) {
  (function(n){
		var title = n.text;
		var note = n.parentNode.parentNode.querySelector("td:nth-child(3)").innerHTML;
		if(note == "-"){
			note = null;
		} else {
			note = parseInt(note);
		}
		arr.push({
			title: title,
			note: note,
			node: n.parentNode.parentNode.querySelector("td:nth-child(3)")
		})
	})(n[i])
};

arr.forEach(function(n){
	if(n.note === null){
		return;
	}
	if(min === null || n.note <= min){
		min = n.note;
	}

	if(max === null || n.note >= max){
		max = n.note;
	}
	total+=n.note;
	count+=1;
	if(noteCount[n.note] === undefined){
		noteCount[n.note] = 0;
	}
	noteCount[n.note] += 1; 
});
console.log("Average: "+total/count);

var center = min + (max-min)/2;
var scale = 10/(max-min);
total = 0;
count = 0;
arr.forEach(function(n){
	if(n.note === null){
		return;
	}
	n.realNote = (n.note-center)*scale + 5;
	total+=n.realNote;
	count+=1;
	n.node.innerHTML+=" / "+(Math.round(n.realNote*100)/100);
});
console.log("Average: "+total/count);