What mechanical thing is mentioned in the first paragraph of "To Build a Fire"?

"To Build a Fire" is one of Jack London's more famous short pieces, and has two versions; the first had a somewhat more optimistic ending in which the main character, an anonymous male fortune-seeker and woodsman, survives his ordeal in the wilderness. The second and more famous version involves the man dying at the end of the story, and this is typically the version that is analyzed in literature courses.
The mechanical device mentioned in the first paragraph is a watch. Watches were fairly expensive tools in that time period (circa 1900), possibly the most valuable thing in terms of monetary value that the man carries, but necessary due to the details provided in the following sentences. In the Yukon (northern Canada), some of which is above the Arctic Circle, the sun won't rise for several weeks during winter, and when it does rise it stays fairly low to the horizon, making traditional time-telling nonintuitive. The remainder of the paragraph explains that there is no sun in the sky, and hasn't been for days, but that the man has grown accustomed to it.