Edit in JSFiddle

angular.module('telavox.test', [])
.controller('MyCommonController', function($scope) {
    $scope.mylist = ['Item 1', 'Item 2', 'Item 3'];
})
.controller('MyListLengthAddedController', function($scope) {
    $scope.myListLengthAdded = $scope.mylist.length + 1;
})
.controller('MyListLengthController', function($scope) {
    $scope.myListLength = $scope.mylist.length;
});

<div ng-app="telavox.test">
    <div data-ng-controller="MyCommonController">
        <div data-ng-controller="MyListLengthAddedController">
            If I added one element, the list length would be {{myListLengthAdded}}.
        </div>
        <div data-ng-controller="MyListLengthController">
            My current list length is {{myListLength}}.
        </div>
    </div>
</div>

</style> <!-- Ugly Hack due to jsFiddle issue: http://goo.gl/BUfGZ --> 
<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.0.6/angular.min.js"></script>
<style>
.error {
    color: red;
}
}