1950s Gruen Airflight "24-Hour Dial"

Gruen was founded in the late 19th century by German immigrant, Dietrich Grun. Based in Ohio, with production primarily handled in Biel/Bienne Switzerland, it at one point had grown to be the largest watch company in the entire US—even larger than household names Hamilton and Bulova—before eventually shuttering its doors forever in 1976. 

One of the brand's calling cards was their close affiliation with the aviation industry, which is where this Airflight comes in. Its unique dial holds a special secret that was especially useful for pilots – it actually tells the time in 24-hour, "military" time. How? The cut-out indices on the dial show the typical 1-12 hour markers until the time hits noon, at which point the hour markers quickly snap to 13-24 markers. For most of us, it's a novelty and a fun talking point, but for a pilot it would've been super helpful – possibly even instrumental in keeping them on course and on time.