Master reference on Omega 30mm, 30t2rg, 30t2 sc rg. http://squelettewatches.com/omega-30mm-chronometres/
Glad I chose to go for a pro subscription at Flickr years ago. Most of the "go-to" threads on WUS (I know... There aren't really a lot of them!) are useless too.
This was such a valuable, well written resource. I hope it comes back up at some point or is archived somewhere. I know I used it extensively in my hunting.
Happy to share Franco has reinstated the 30mm Chronometer bible: http://squelettewatches.com/omega-30mm-chronometres/