Can directive isolated scope be used inside directive for calculations - angularjs

Question

If there is a directive defined can the scope passed to it through attributes, defined on it, be used inside this directive to get needed results for usage in template? i.e. I have such directive
var carAuction = angular.module('carAuction');
carAuction
.controller('mainCtrl', function($scope)
{
var car = {
comments: []
};
car.comments.push({
comment: 'Ok car',
rating: 1
});
car.comments.push({
comment: 'Nice car.',
rating: 2
});
car.comments.push({
comment: 'Awesome car!',
rating: 3
});
$scope.car = car;
})
.directive('carCommentRaiting', function()
{
return
{
restrict: 'E',
templateUrl: 'path/to/template.html',
scope:
{
value: '=value',
maxValue: '=max-value'
}
};
})
.filter('range', function()
{
return function(input, total)
{
total = parseInt(total);
for (var i=1; i<=total; i++)
{
input.push(i);
}
return input;
};
});
In html part I have
<div>
<div ng-repeat="comment in car.comments">
Rating: <car-comment-raiting value="comment.rating" max-value="10"></car-comment-raiting>
</div>
</div>
template.html
<div>
<ul class="list-inline">
<li ng-repeat="n in [] | range:value"><span class="glyphicon glyphicon-star"></span></li>
</ul>
</div>
And I want to pass additional value to the template which should be calculated as maxValue - value. Haven't found any example describing that. Thought about using link property, but description tells, that it is used for other purpose.
UPD:
I was able to fix it with
return {
restrict: 'E',
templateUrl: 'path/to/template.html',
scope:
{
value: '=',
maxValue: '='
},
controller: function($scope)
{
$scope.calculated = $scope.maxValue - $scope.value;
}
};
but for some reason it doesn't work all the time. One time it works and the other time calculated variable is null.

Answer 1

All calculations must be done inside a direcitve link function or in controller.
Here is example with directive:
.directive('carCommentRaiting', function() {
return {
restrict: 'E',
template: 'path/to/template.html',
scope: {
value: '=value',
maxValue: '=max-value'
},
link : function(scope, element, attr) {
scope.calculated = scope.maxValue - scope.value;
/// watch value to update calculated on value update:
scope.$watch('value', function(newValue){
scope.calculated = scope.maxValue - newValue;
});
}
};
});