function amDifferenceFilter(value, otherValue, unit, usePrecision) {
					if (isUndefinedOrNull(value)) {
						return '';
					}

					var date = amMoment.preprocessDate(value);
					var date2 = !isUndefinedOrNull(otherValue) ? amMoment.preprocessDate(otherValue) : moment();

					if (!date.isValid() || !date2.isValid()) {
						return '';
					}

					return date.diff(date2, unit, usePrecision);
				}
@ngdoc filter
@name angularMoment.filter:amDifference
@module angularMoment