The present Aero-Compax is a remarkable and rare example featuring a water-resistant screw-down case back. Very few examples are known to the market. One is depicted in a print advertisement from circa 1947. The Aero-Compax was marketed to pilots who wanted to mark a specific time. The top register had an hour and minute hand that could be adjusted by a crown on the left side of the case. It was often used to mark the time of departure for a plane or the time something should occur. It was a feature particularly useful before the introduction of the Vulcain Cricket in 1947 that allowed for someone to have a wristwatch with a loud alarm.