Patek Philippe Calatrava Pilot Travel Time Ref. 7234G
A watch with the second time zone feature is equipped with either a mechanism or device that is able to display the time in another time zone. Add-on features may include the date of the second time zone and/or the day and night indication for that time zone.
Such dual-time watches are commonly described as GMT watches even though the acronym refers to the time zone with the offset UTC + 0. Offsets are the time differences between a particular time zones and UTC.
If the time offset is a plus, it means that hours are to be added for time zones to the east of the prime meridian and a minus for time zones to the west of the prime meridian. For example, both Singapore and Malaysia are to the east of the prime meridian and in the UTC + 8 hours time zone.
The UTC offset for these two countries was adopted on 1 January 1982. Prior to this, the standard time for Singapore and Malaysia was UTC + 7.30 hours. Both countries even used Daylight Saving Time and had odd UTC offsets such as UTC + 7.20 hours.
Interestingly, while the geography of China spreads across five time zones, the country has only one official time zone in use: UTC + 8.
Using a bezel with twelve hour markers and referencing the hour hand is one method of indicating a second time zone. An additional central hour hand for the second time zone that completes one rotation every 24 hours referenced with the corresponding hour marker on a rotating bezel’s 24-hour scale is another common system used.
If one were to set the hour hand or indicator for the second time zone in sync with UTC or GMT, all that is needed is the time offset of any country that is mentally added or subtracted that with UTC accordingly, and its time can be told. If used in such a manner, this will theoretically be a “true” GMT watch.
One classic second time zone watch that is highly popular is the Rolex GMT-Master II.
When travelling and in a different time zone, the time at the current location is known as local time while home time is the time at the place one had travelled from and is generally the time zone where one resides in.