Using a GMT and other background info

[MikenAZ]

I Purchased a 16750 GMT Master in the 80s while on TDY with the USAF. I like the fact you can keep your home time and rotate the bezel to the time zone your in or going too. Yes.. with today's cell phones and advanced avionics suites available for aircraft some may believe the watch is past its prime. I still wear my GMT and recently acquired my father inlaw's 16700. Both share wrist time and I will gladly pass these to my sons when the time comes.

[pa30crewchief]

I need (and enjoy!) the ability to read more than one time zone at any given time in my work. Its become a bit of an obsession in my collecting and there are a few more GMTs at home.

Anyways below is exactly the same time set for my home time (Dubai) and my present city (Seoul).

From left to right a Glycine Airman (1960?), Rolex GMTIIc BLNR (2016), Rolex Explorer II (2010) and Benrus Type I Class A (1974).




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[Old Expat Beast]

That Benrus looks great. I'm a big fan of 12 hour bezels for tracking time. Really easy to read. Sadly I only have one.

[HogwldFLTR]

Seems to me the original write-up in this thread is very GMTIIcentric. The original GMTs only tied the GMT hand to the 12 hour hands and they were always in sync. It makes no sense to always have the GMT hand set to Zulu time as it is then confusing to read the time at a glance. It makes more sense to move the bezel to Zulu time and use the 12 hour clock for local time. Just my simple observation owning a 16700.

[skydriver]

Nice information, but I just like mine for how it looks.

[Lordofrolex]

Thanks for the info

[Tools]

Originally Posted by HogwldFLTR

Seems to me the original write-up in this thread is very GMTIIcentric. The original GMTs only tied the GMT hand to the 12 hour hands and they were always in sync. It makes no sense to always have the GMT hand set to Zulu time as it is then confusing to read the time at a glance. It makes more sense to move the bezel to Zulu time and use the 12 hour clock for local time. Just my simple observation owning a 16700.

It's just an interesting perspective with a small smattering of history thrown, and yes, the OP only seems to be familiar with the much later GMT II.

It's not a GMT hand, it's a 24 hr hand. GMT is the name of the watch which was originally meant to have the bezel rotated to show GMT time at a glance on the 24 hr bezel (or any other zone). You are right; it would make little sense for a pilot to set their watch to show Zulu on the standard dial when they only use that for 10% of their time.

Read it as in interesting Thread, but not a research document..

[Base-Z]

Yes, no wrong answer. Being an astronomer, I have my GMT watch set to Greenwich
mean astronomical time (GMAT).

[ched]

Thanks for the great detail on the GMT! I'm actually looking to purchase one soon.

[Bluside]

Also a retired airline pilot here...I always keep the 24 hr. hand to GMT.

Now that I'm retired, it does not matter. Just habit though.

[rolexwee]

Originally Posted by SmokieDaBear

Hello,

I am new to the forums and the brand new owner of a "batman" GMT Master II. I love it. Wear it every day.

Quick question. I thought the GMT hand should be positioned at your local time. For example, I live in EST. When I travel I can put the local time on my watch using the hour and minute hand. That way it is much easier to set. So I have local time and EST on the "GMT" hand.

Does that make sense? For a traveler like myself it is more useful because I can look to see what time it is at home and know what time it is at my location.

First off technically you don't live in EST. You live in a place that uses the US East Coast rules. Right now EDT rules are used. EST rules are used in the winter.

The GMT hand is made to be set to GMT. Set it to GMT / UTC. Then to find out what the time is in East Coast time during the summer (EDT), move the bezel 4 times to the right. For the 4 hours EDT is behind UTC. In the winter it is 5 hours. If you want to find out what the time is on the west coast, you move it 3 steps more to the right.

Here is a video that explains it: https://www.youtube.com/watch?v=RG4cZPgN9Oc

[janice&fred]

Originally Posted by skydriver

Nice information, but I just like mine for how it looks.

we have both early GMT as well as later GMT II's in our collection and find the OP as well as others' contributions in this thread on the uses and functions interesting, but for me utilizing these features would be way too intellectually taxing. i just wanna wear the thing

[oldsalt]

Originally Posted by Bluside

Also a retired airline pilot here...I always keep the 24 hr. hand to GMT.

Now that I'm retired, it does not matter. Just habit though.

Same here...
cheers

[Olienh]

Thank you so much for this information! I am looking at the GMT II BLNR as my first Rolex. I was comparing this watch against the SubC Hulk, but being a business traveler, the GMT seems to have more function that I could use. I didn't understand the significance of the two-color bezel until I read this. It adds great looks AND great functionality.

Cheers!

[VinnieVegas]

Originally Posted by SmokieDaBear

Hello,

I am new to the forums and the brand new owner of a "batman" GMT Master II. I love it. Wear it every day.

Quick question. I thought the GMT hand should be positioned at your local time. For example, I live in EST. When I travel I can put the local time on my watch using the hour and minute hand. That way it is much easier to set. So I have local time and EST on the "GMT" hand.

Does that make sense? For a traveler like myself it is more useful because I can look to see what time it is at home and know what time it is at my location.

When I first got my 16710, I set the 24 hour hand to GMT time, mostly out of convention.

Somewhere along the line, I just decided to set it to my home time (Eastern), and when I travel I set the hour hand to local time and the 24 hour hand to home time. Makes it easy and functional without turning the bezel.

[jrs146]

Originally Posted by VinnieVegas

When I first got my 16710, I set the 24 hour hand to GMT time, mostly out of convention.

Somewhere along the line, I just decided to set it to my home time (Eastern), and when I travel I set the hour hand to local time and the 24 hour hand to home time. Makes it easy and functional without turning the bezel.

That's what I do. I have no need for UTC time, but It's very handy to set the hour hand to local and 24 hour to home time.

[T. Ferguson]

Originally Posted by rolexwee

...The GMT hand is made to be set to GMT. Set it to GMT / UTC. Then to find out what the time is in East Coast time during the summer (EDT), move the bezel 4 times to the right. For the 4 hours EDT is behind UTC. In the winter it is 5 hours. If you want to find out what the time is on the west coast, you move it 3 steps more to the right.

The GMT hand was made to be set to UTC? Since when?

[raymz]

very nice write up, thanks for sharing.

[raulfragoso]

I have a slightly different use for the GMT hand, since I live in Brazil and work for a company in Australia, I always have the GMT set to the time in Oz.

[Tools]

Originally Posted by T. Ferguson

The GMT hand was made to be set to UTC? Since when?

Yes, clearly that poster is not familiar with the GMT watch history and believes that you-tube is a research source..

[Longhorn02]

Current airline pilot here, and I have to say having the GMT hand set to UTC helps me out all the time when at work when quickly browsing the release for the next flight. Weather reports, departure times (on our paperwork) is always in UTC and just being able to glance at the watch to decode the weather times, NOTAM valid times, and time until next departure is incredibly helpful. Then on the overnights I just rotate the bezel to show the local time zone for the night and then it gets recentered the next morning when we show for work again!


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[fosbibr]

While not a pilot, I seem to travel almost as much as one and have two GMT's (root beer and BLRO) as well as an EXP II to keep track of home time when travel.

Thanks for the write up.

[BravoOne]

Originally Posted by petespendthrift

In the original post I talked briefly about the GMT2 and some general information on the significance/history of Greenwich Mean Time, Latitude and Longitude and timezones. For nostalgia here is an old ad that is fun and interesting.

A 1961 advertisement for the Rolex GMT in which they specifically talk about it's useful features. The photo shows the Sextant (probably on a Boeing 707) that was used through a periscope in the cockpit roof. An accurate GMT time source is essential for using a sextant as every 4 seconds of time keeping error equates to approximately a nautical mile of inaccuracy. Of course navigators and sextants are no longer used on modern airliners (with IRS and GPS) but a well regulated watch and also a GMT reference is still a very useful convenience both on and off the aircraft.

A little off topic but that is certainly not a 707. Don't ask me how I know:)

[strafer_kid]

Originally Posted by skydriver

Nice information, but I just like mine for how it looks.

Sums it up very nicely...GMT is just a super looking watch in virtually any version!

[Lartamia]

I love wearing my GMT while traveling to an other time zone. There is always a smile on my face when I set the time arriving in a new time zone.

Nice story and nice to read everytime

[CoachLange]

Great write up Loved seen the Rolex ad, too.

[Lhn5]

It seems like one can't actually read three time zones at once. As an example if you have the 24 hour hand set to Zulu but then move the bezel for a different time zone you are losing you Zulu time unless you move the bezel back to neutral. Then again why would a pilot, or especially a non pilot need 3 time zones in front of them anyway? I have the regular 12 hour hand on local time now and the 24 hour hand in a nearby time zone where relatives live. When I travel I would expect to change the 24 hour to home time and the 12 hour hand to local travel time and never move the bezel. Am I not taking full advantage of gmt 2 capabilities?

Also still didn't find in the manual how to get my emails through it, just kidding.

[Nikrnic]

Originally Posted by petespendthrift

The GMT-2 is a popular watch but it seems some people don’t understand exactly what it does so here is an explanation (it’s as simplified as possible).

The watch minutes and 24 hour hand are designed to be set to GMT (Greenwich Meridian Time) - now often referred to as UTC (Universal Time Co-Ordinate).

Some centuries ago when astrologists were developing their knowledge of planetary motion and the solar system, Greenwich near London in England was the site of a major observatory. The astrologists there worked out the system of Latitude and Longitude used today that enables us to navigate around the planet by sea and air.

As the planet is a globe, Lines of Latitude called parallels run East/West like horizontal slices through the planet and lines of Longitude (called meridians) run North/South and are like segments of an orange - joining each other at the Poles.

The meridians are numbered in measurements of degrees, with zero degrees being the one that passes through Greenwich, England. The lines then count upwards to 180 degrees if you head either East or West. The meridian at 180 East is the same as that for 180 West - where the counting up meets on the opposite side to the planet from Greenwich (called the Greenwich anti-meridian and used as the international date line).

One degree of Latitude - North or South is equal to 60 nautical miles. One degree East or West at the Equator is also 60 nautical miles but as these lines divide the planet up like orange segments the distance between them gets smaller as you move away from the equator. Near the poles, where all meridians join, 1 degree clearly become no distance at all.

The sun rises in the East and sets in the West. At 1200 GMT the sun is at it's highest point in the sky directly overhead Greenwich.

GMT is the official time at the zero Meridian (Greenwich Meridian).

For every 15 degrees of longitude you travel West the sun will reach the point directly overhead exactly one hour later when compared to 1200 GMT. Likewise for every 15 degrees East that you travel the sun will reach this mid-day point an hour earlier compared to GMT mid-day.

Knowing this actually made it possible to use measurement of the Suns angle in the sky at a given time to calculate where a ship was (in Longitude ie. East/West) so long as the ship had an accurate clock called a chronometer set to GMT.

Time was based on 1200 being the mid-day point wherever you actually were so there were hundreds of different time zones in each country. Later with the advent of trains and travel it became impractical to have a town just a few miles away on a slightly different time zone (making time tabling of the trains extremely complicated!).

All countries eventually adopted what is known as a standardised time system so that whole regions now use the same time zone based upon the regions approximate distance from the Greenwich meridian and generally using changes of whole hours - from GMT (rather than complicated part hour changes). The time zones are named in a way that indicates their difference from GMT which is know as zero or Zulu (eg. +4 or -4 or equivalent letters).

However once aircraft were invented that could cross multiple regional time zones at high speeds the problem was back again and not so easy to solve. Taking off in one zone, then flying through a number of others before landing in yet another different one creates serious problems when co-ordinating with air traffic control etc. So all international aviation uses GMT (now called UTC) to prevent confusion over times. All flight plans are made using GMT.

Once the 24 hour hand and minutes are set to GMT on a Rolex GMT2 they do not need to be adjusted and can be used to tell GMT anywhere in the world. So that the pilot can also have local time and date set on his watch, he simply pulls out the crown to the first position and jumps the (normal) “local” hour hand backwards or forwards as appropriate in one hour intervals. The seconds, minutes and 24 hour hand continue to run, so accuracy is not lost. Moving the “local” hour hand backwards or forwards through midnight jumps the date backwards or forwards appropriately (do not do this on non GMT watches, it breaks them), so the local date can also be shown.

If the pilot would like to temporarily show the time in a third time zone he can rotate the bezel either direction by the appropriate amount of hours of time offset. The 24 hour hand will now point to the third time zone (and can be returned to GMT easily when finished).

For quick reference the bi-colour bezels also shows at a glance whether the third time zone or GMT (whichever is set) is in daylight or darkness giving an quick indication of what part of the day it is in that time zone. Rolex GMT-1 models do not have an independently adjustable “local” hour hand and so have to rely solely on the turning bezel to calculate GMT from local 24 hour time.

The first Rolex GMTs were made on contract for Pan American Airways and issued to their pilots. They subsequently become the watch of choice for both military and commercial pilots.

The popularity of the Rolex GMT amongst pilots has always been that it is a simple and robust watch that provides clearly legible and useful information without any unnecessary extras.

Following NASAs use of the Omega Speedmaster Moon Watch, chronographs also became popular with pilots although they were originally associated with motorsports. Breitling and others have very successfully marketed their chronographs as “real” pilots watches and the general public these days often think that a pilots watch has to be a chronograph.

Most commercial and military pilots will admit that a chronograph is of little use in an aircraft cockpit as a navigation timer as they are generally too hard to read whilst flying due to the small subdials and also not easy to refer to regularly as part of a scan of all the aircraft main instruments whilst worn on the wrist. Aircraft nearly always have a proper timer included in the cockpit instruments. Pilots however love their toys so the chronograph remains popular amongst them.

So now, if you own a Rolex GMT and one day find yourself bragging to your friends in the bar that it’s a pilots watch and they disagree (because it’s not a Breitling Chronograph) you can tell them that it is the original classic and the real deal - not just for posing with - even though that might be exactly what you are using it for!

Now for sure I'll stick to my 3 hander, hehe but I get it, good article

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[prozac51]

Originally Posted by petespendthrift

Moving the “local” hour hand backwards or forwards through midnight jumps the date backwards or forwards appropriately (do not do this on non GMT watches, it breaks them), so the local date can also be shown.

An acquaintance of mine once proudly showed off his GMT look alike bought online for 'thousands less than your Rolex'. I challenged him to set his bezel and hour hand quickly and accurately, alternating between + and - timezones then change the date backwards and forwards repeatedly. Needless to say his watch ended up being sent back for warranty repair...

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[holdtime]

Originally Posted by longhorn02

current airline pilot here, and i have to say having the gmt hand set to utc helps me out all the time when at work when quickly browsing the release for the next flight. Weather reports, departure times (on our paperwork) is always in utc and just being able to glance at the watch to decode the weather times, notam valid times, and time until next departure is incredibly helpful. Then on the overnights i just rotate the bezel to show the local time zone for the night and then it gets recentered the next morning when we show for work again!


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