The type 20 5101/54 (signifying the number and year of the contract) was usually made with a large ballshaped crown, enabling the watch to be rewound by a pilot whilst wearing gloves. However, any advantage gained by making the watch easy to wind, was generally outweighed by the problems of the button catching on clothing under rough conditions, and the majority have been fitted with a more conventional windingcrown. The title retour en vol, refers to the instantaneous flyback feature of the chronograph work. A single push on the lower chronograph button, zero's the chronograph hand whilst still in motion, which then restarts immediatly. Avoiding the need for a pilot to break concentration from the controls of the plane.