I am interesting in buying my first Omega watch which would be the Seamaster Aqua Terra with either 38mm or 38.5mm case. It appears that there are two almost identical models (apart from the different date window positions and dial patterns) with different movements which are:

1). AQUA TERRA 150M - OMEGA CO-AXIAL MASTER CHRONOMETER 38 MM - 220.10.38.20.03.001 - OMEGA Master Chronometer calibre 8800
2). AQUA TERRA 150M - OMEGA MASTER CO-AXIAL 38.5 MM - 231.10.39.21.03.002 - OMEGA Master Co-Axial calibre 8500

My question is what are the differences in terms of the movement apart from the differences in the power reserve?

Please help, thanks!

 

Aside from the mainspring differences, the 8500 also has a quick-hour adjust, which lets you move the hour hand in 1 hour increments with the crown set to the middle position. That comes in "handy" when traveling (see what I did there?) as you can quickly set to the new time zone without having to re-hack your watch. The downside of this is to set the date, you must move the hour hand around the dial twice for each incremental advancement of date. However, this can still be done relatively quickly. The 8800 date adjusts quickly in the forward direction with the crown in the middle position, like most other 3 hand + date watches out there.

You can see the quick-hour adjust feature of the Omega cal. 8500 here, at 2:40 in this guy's video.

 

Thank you so much for such detailed information

 

I’d wash the movement differences. The watches have slightly different proportions. I’d try them on and see which you like better.

 

I have tried both but can't make my decision yet haha. I think both may be able to do the date advance function (80% sure). The crown designs/guards are different as well. The funny thing is 8500 has more power reserve at 60 hours than 8800 with 55 hours. Additionally, according to the Omega website, 8500 "is resistant to magnetic fields greater than 15,000 gauss" when 8800 is "resistant to magnetic fields reaching 15,000 gauss". The only rather "superior" specification for 8800 is it is METAS certified.