 Jaeger, the Duoplan was built on two levels – hence its name – enabling it to maintain a large-size balance.The Duoplan was also one of the first gem-set steel watches and, in 1929, its glass was replaced with sapphire crystal, a first in watchmaking.The Duoplan was ensured by Lloyd's of London with a special after-sales service, and a damaged movement could be replaced in a few minutes, leading London-based store owner Tyme to display in its shop window