I really have a weird problem in adding two numbers.

Here is my code, in the first controller everything is working fine, but in the second controller instead of 0 if I add 10, the output is completely weird

Here is html code

<div ng-app="">
<div ng-controller="Controller1">
    <br/>**** Controller-1
    <br/>Add 0 : {{update1(0)}}
    <br/>Add 10 : {{update1(10)}}
    <br/>Add 50 : {{update1(50)}}
    <br/>Add -60 : {{update1(-60)}}</div>
<div ng-controller="Controller2">
    <br/>**** Controller-2
    <br/>Add 10 : {{update2(10)}}
    <br/>Add 10 : {{update2(10)}}
    <br/>Add 50 : {{update2(50)}}
    <br/>Add -60 : {{update2(-60)}}</div>
</div>

Here is my javascript

function Controller1($scope) {
var x = 0;
$scope.update1 = function (smValue) {
    x += parseInt(smValue);
    return x;
}
}

function Controller2($scope) {
var y = 0;
$scope.update2 = function (smValue) {
    y += parseInt(smValue);
    return y;
}
}

and here is the output

**** Controller-1 
Add 0 : 0 
Add 10 : 10 
Add 50 : 60 
Add -60 : 0

**** Controller-2 
Add 0 : 110 
Add 10 : 120 
Add 50 : 170 
Add -60 : 110

here is the link to try: http://jsfiddle.net/6VqqN/

can anyone please explain me why it is behaving like that. Even if I add a 3or4 digit number, output is completely different then what I expected.