Add `val` to the current value.

        :type val: int
        :param val: Value to add.

def add(self, val):
        """Add `val` to the current value.

        :type val: int
        :param val: Value to add.
        """
        if not isinstance(val, six.integer_types):
            raise ValueError("GaugePointLong only supports integer types")
        with self._value_lock:
            self.value += val