Answer:
a somewhat confusing term applied to a high quality- above the normal type- Pocket Watch with a chronometer rating. Probably the best example was the Jules Jurgensen Marine- which was portable (but usually kept in a glass-fronted box when On Deck on a ship) The JJM was popular with ALL Scandinavian polar explorers and they used the slogan, with a Polar bear in the background ( magazine ads) On Top Of The World. The JJ watches, were first cabin throughout- and were also chosen by the Romanov family for personal as well as service use. Anastasia had a customized ( Gold and platinum case with her monogram) Jules Jurgensen All-Services. It survives in a museum. If they ever make another movie ( live) about her- what a splendid prop. the Explorer and Russian contrat Jules Jurgensens were made in Copenhagen, not at their Swiss plan.t