A Traveler GMT, or True GMT, has a separate 12-hour hand for adjusting local time zones while traveling. For instance, when in New York, both time zones can match, but in Hong Kong, you can change the local hand without affecting the other hands, keeping track of time back in New York. A Caller GMT, or Office GMT, features a separate 24-hour hand, ideal for those working across different time zones. For example, if you’re in New York with offices in Hong Kong, you can easily set the 24-hour hand to show 13 hours ahead without disturbing the other hands.