While ceiling fan manufacturers (mainly Emerson) have had electrically reversible motors in production since the 1930s, most fans made before the mid-1970s are either not reversible at all or mechanically reversible (have adjustable blade pitch) instead of an electrically reversible motor. In this case, the blades should be pitched to the right (or left if the motor spins clockwise) for downdraft, and to the opposite side for updraft. Hunter's "Adaptair" mechanism is perhaps the most well-known example of mechanical reversibility. In very rare cases, fans are both mechanically and electrically reversible, allowing for the fan to push air in either direction, while rotating either clockwise or counter-clockwise.