How to trace source of $watch model updates in AngularJS?

In my multi-user AngularJS app, I have a model object on my scope. This model can be manipulated by both user input and server updates.

I have a $watch observer to track the model and update the UI. Is it possible to determine the source/reason of my model update from within my $watch function? Without that check, I have problems with feedback loops (e.g. UI→Server→UI).

UPDATE: some code

Controller:

$scope.elementProperties = { left: 0 };

$scope.$watch('elementProperties.left', function(newVal, oldVal) { changeSelectedElementProperty('left', newVal, oldVal); } );

Directive:

angular.module('myapp.ui-editor').directive('myappPropertiesPanel', function () {
    return {
        templateUrl: 'views/ui-editor/myappPropertiesPanel.html',
        restrict: 'A',
        scope: { elementProperties: '=' },

        link: function postLink (scope, element, attrs) {
            scope.$watch('elementProperties.left', function(newVal, oldVal) { console.log('PropertiesPanel change left', newVal, oldVal); } );
        }
    };
});