The Amazing In-House Xi Movement
Since all three of these watches are based on the same movement, let's start there. The in-house ξ (Xi) movement is a real thing of beauty. It has subsidiary seconds at 6 o'clock (which can be stopped when setting) and two coupled rings for telling time in the second timezone - one small ring at 3 o'clock for telling the time and one larger ring that runs the full perimeter of the movement that indicates the location of the second timezone. Finishing on the Xi is extremely high quality, as you would expect from Nomos, and the partially cut-out rotor allows you to still admire much of the movement through the sapphire caseback on all three models.
Second Timezone Indicator On Both Tangomat GMTs
Nomos Tangomat GMT City Code Timezone Indicator
Nomos Tangomat GMT Plus +/- GMT Timezone Indicator
While on the the Zürich Weltzeit the larger timezone ring is fully exposed and is styled as a worldtimer cities ring, both Tangomats keep the ring concealed except for an aperture at 9 o'clock. The biggest difference between the Tangomat GMT and the Tangomat GMT Plus is how this ring indicates the second timezone. The GMT uses three-letter city codes while the GMT Plus uses the number of hours +/- GMT for the timezone. The actual time ring at 3 o'clock functions almost exactly the same on all three models, though it too is a little more covered up on the Tangomats.
The Architectural Tangomat Case
Another obvious difference between the GMT models and the Weltzeit is the case choices and aesthetic styling of the watches. The Weltzeit is packaged in the curved and classic looking Zürich case, with flowing lugs and a round pusher at 2 o'clock. The GMTs on the other hand feature the Tangomat case, which is much more rigid and architectural than the Zürich. The case sides are steep, the lugs are angular and arching, and the round pusher is swapped for a rectangular one. The GMTs also have a much bolder, more traditionally Nomos-looking dial, with a lot more white space.
All three of these GMT watches are outstanding and present immense value for money. The Tangomat GMTs are both priced at $4,570 and the Weltzeit is $5,760, and you get beautifully finished, in-house GMT movements in very stylish packages. But which of the three you prefer is entirely a matter of taste.