Text by Shigeru Sugawara
Although the functions and display styles of GMT, dual time, and world time watches vary, they have all been treated as watches based on the GMT mechanism because, to reiterate, they are based on the basic principle of the world's 24 time zones (time zones) and one-hour time differences. However, there is one point that we have not touched upon so far: how minutes are handled. In the world time system for watches, even if there are time differences depending on the region, minutes are considered to be the same everywhere. For example, if Tokyo and Paris are eight hours apart, if it is 8:10 PM in Tokyo, it is 12:10 PM in Paris, so the ten minutes are the same.
In models with a single minute hand, the minute hand is used to read both the home time and local time, regardless of the time zone. In dual time models with two time displays on the dial, each with its own minute hand, the two minute hands are always linked and cannot be moved arbitrarily.
In the real world, there are currently around 40 standard times based on UTC (Coordinated Universal Time). Some of these regions have set "minute differences" of 30 or 15 minutes. Currently, 30-minute differences are found in French Polynesia, Newfoundland, Canada, Venezuela, Iran, Afghanistan, India, Sri Lanka, Myanmar, North Korea, central Australia, and Lord Howe Island, while 15-minute differences are found in Nepal, Eucla, Australia, and Chatham Island, New Zealand. However, the standard time adopted in each region may change due to political reasons.
Mechanical GMT watches based on the GMT mechanism could handle time differences in increments of one hour, but they did not go so far as to precisely handle minute differences. Rather than being technically impossible, it was thought that since 24 time zones cover almost all the times in major cities around the world, there was no need for a practical function that covers more than that in a mechanical watch.
