question on terms to describe GMT 1675

[lis]

what's a Mark 1 dial?
and what does it mean when description says correct open 6 and 9 date wheel?
did a google search and couldn't quite find it, figure here are the experts!

[ahnets]

I am not an expert, but I once had a similar questions and through help of TRF members got some basic understanding. So I'm paying it forward :-)

Mark 1 dial on GMT 1675 is found on "case series from around 1.6 mil until about Mid 2 mil or so..." Very good overview of different dials in this thread:
http://www.rolexforums.com/showthread.php?t=74976

Open 6 and 9 example date wheel example - notice how the 6 and 9s fonts are the only ones do not fully close. Depending on the serial of the watch you're looking at it should either come with open 6 and 9s or closed ones. It's basically a way of telling if the date wheel is correct to the watch or a replacement. Usually open 6 and 9 wheels are silver-ish in color and for watches pre late 1970s, while closed 6 and 9s are white and made in late 1970s to early 80s onwards. Basically if you're looking at a watch that is from the 60s and and it has a white, closed 6 and 9 wheel it probably means the wheel is a replacement and not original to the watch. Here some some further open 6 and 9 examples.

Here is an example of a closed 6 and 9s date wheel for you to compare.

As always there is debate as to whether open vs closed matters or not, and when the transition began etc. Ultimately it comes down to personal preference and whether it matters to you.

[lis]

very helpful! thanks. really great to be able to up my knowledge.