What is the 24-hour watch?

Watch with a 24-hour analog dial have an hour hand that makes one complete revolution, 360°, in a day (24 hours per revolution).
The more familiar 12-hour analog dial has an hour hand that makes two complete revolutions in a day (12 hours per revolution).

Twenty-four-hour analog watches are used today by pilots, scientists, and the militaries, and are sometimes preferred because of the unambiguous representation of a whole day at one time. Note that this definition refers to the use of a complete circular dial to represent a 24-hour day. Using the numbers from 1 to 24 to mark the day is the 24-hour watch system.