The year 1939 is marked by the submission of the sidereal time-keeper patent. This goes hand-in-hand with the will of accompany now submerged in the world of aviation, in keeping with the spirit established previously by Breguet with the navy. The sidereal time-keeper - or siderometer – is a precious instrument panel tool, of which about thirty units were purchased by the French Air Force and by the airline Air France.