Dr. Ito's thorough analysis of mechanical watches!! Vol.25 ~ What is the correct way to use a GMT Master? ~

Good evening, everyone!

In this column, I discuss mechanical watches from an engineer's perspective. For the 25th installment, the theme is:

"What is the correct way to use the GMT-Master?"

I will be discussing this topic.

It's no exaggeration to say that the ROLEX "GMT-Master" is as popular as the Daytona.

Its biggest feature is the GMT function, which displays a second time zone. The "GMT-Master II" series, which is the successor to the "GMT-Master," can even display a third time zone.

However, it's also true that we often hear people say, "I can set the second time zone, but how do I set the third?" and many people are not very familiar with it.When I reviewed the operating instructions myself,I realized it was indeed a bit complicated.

So, this time, I will explain the operation of the "GMT-Master" in detail using images. If you are considering purchasing a "GMT-Master" or "GMT-Master II," please use this as a reference.

How to use the "GMT-Master"

First, let's look at the "GMT-Master." The "GMT-Master" has the following features:

• It has a "GMT hand" that displays a second time zone or acts as a 24-hour hand.
• The "GMT hand" moves in conjunction with the hour and minute hands and cannot be moved independently.
• The bezel can be rotated both left and right.
• It has a quick-set date function (for reference numbers with 5 digits or more).

With this understanding, let's take a look!

Let's use Japan and New York (14-hour time difference) as an example to display the time in two countries.

Assume the time in Japan is 10:00 AM. In that case, it would be 8:00 PM (the previous day) in New York.First, align the ▼ on the bezel with the 12 o'clock position.

In this state, the GMT hand acts as a 24-hour hand.

Next, set the hands to New York time.
Since New York is 14 hours behind Japan, move the hands back 14 hours.

The date changes, and it becomes 8:00 PM the previous day.

Next, rotate the bezel by the amount of the time difference.
Since Japan is 14 hours ahead of New York, turn the bezel 14 hours to the left.

The important thing to note here is that the bezel makes a full rotation in 24 hours, not 12 hours.

From the hour and minute hands, you can read the time in New York (8:00 PM), and from the GMT hand and rotating bezel, you can read the time in Japan (10:00 AM).

Also, if you want to read the time in Japan with the hour and minute hands and the time in New York with the GMT hand, simply turn the bezel 14 hours to the right.

How to use the "GMT-Master II"

Now, I will explain how to use the "GMT-Master II."

The "GMT-Master II" has the following features:

• It has a "GMT hand" that displays a second time zone or acts as a 24-hour hand.
• Only the hour hand can be moved independently.

• It does not have a quick-set date function. The date is adjusted by rotating the hour hand.
• The bezel can be rotated both left and right.

Similar to before, let's use Japan and New York (14-hour time difference) as an example to display the time in two countries. We will set the time to 10:00 AM in Japan and 8:00 PM in New York.

Align the ▼ on the bezel with the 12 o'clock position.
Next, confirm that the hour hand and the 24-hour hand (GMT hand) show the same time.

*In the photo above, the hour hand points to 10 o'clock, and the GMT hand also points to "10" on the bezel, indicating the same time.

If they are not showing the same time, align the GMT hand to the 24-hour position, then rotate the hour hand to align with midnight. Then, advance the time to the current time to synchronize them.

Next, set the hands to New York time.New York is 14 hours behind Japan, so pull the crown out one click and move only the hour hand back 14 hours.

The hands will point to 8:00 PM, and the date will revert to the previous day.The GMT hand will point to "10" on the bezel, indicating Japan, the second time zone.
　
Furthermore,the GMT-Master II can display a third time zone by rotating the bezel.Let's try displaying the time in Hong Kong, in addition to Japan and New York.

Since Hong Kong is 1 hour behind Japan,turn the bezel one hour to the right.

Then, you can read three different times:

• From the "minute hand" and "hour hand," the time in New York is 8:00 PM.
• Looking at the "GMT hand" in 24-hour format, the time in Japan is 10:00 AM (read from the position of the GMT hand, not the numbers on the bezel).
• Furthermore, from the "GMT hand" and the "24-hour bezel," you can see that the time in Hong Kong is 9:00 AM.

That might have been a bit difficult, but how was it? While you might not often need to check a third time zone, knowing how to use it like this will give you peace of mind no matter which country you visit.

Summary

How was it? 

The "GMT-Master" and "GMT-Master II" are quite difficult to understand when explained in words, but I hope that with the accompanying images, you were able to grasp it. Please refer back to this article many times and take this opportunity to learn how to use it!

I hope this article was useful to you all and that it piqued your interest in luxury watches, even a little! Also, if you have any questions, please do not hesitate to ask us directly; we will be happy to answer them, so please feel free to visit or contact us.

Look forward to the next time! See you then!