A brass bell that is used aboard ships to ring the watch. It is rung every half-hour to let sailors know when it's time to rotate within their watch.

The first bell is rung half an hour after the watch begins. It is a single stroke of the bell. Every half-hour thereafter, the bell is rung again, each time adding another stroke. Thus, one hour after the watch begins, the bell is sounded twice, known as "two bells". This continues until the end of the watch, which is "eight bells".

In order to make the number of bells clearer, they are sounded in groups of two. Thus, four bells is sounded as "ding-ding, pause, ding-ding".

As with every rule, there is an exception. Between 1600 and 2000 (4 and 8 PM to landlubbers), there are two dogwatches. Basically, these are half-watches to ensure that you won't always get stuck with the night watch. (see Naval Watchkeeping). The end of the first dogwatch is four bells. However, the first half-hour of the second dogwatch is one bell. The end of the second dogwatch is 8 bells.

So it goes something like this:

• 1600 - eight bells (end of the afternoon watch)
• 1630 - one bell
• 1700 - two bells
• 1730 - three bells
• 1800 - four bells (end of the first dog watch)
• 1830 - one bell
• 1900 - two bells
• 1930 - three bells
• 2000 - eight bells (end of the second dog watch).

The reason for this is twofold. For one, 1830 is at the beginning of a watch, even if it isn't a full watch, and thus deserves the reset back to one bell. On the other hand, 2000 is the end of a full watch, and thus deserves a full eight bells.