As Trapi said, this model is a mix between the Richard Lange "Pour le Mérite" and the 1815 model.
The difference with the 1815 is the seconds dial. It doesn't have the numbers and it's a little higher, letting visible the lower part of the 6.
Here is a picture
From the Richard Lange "Pour le Mérite" point of view differences are bigger, starting with the numbers in the dial, which are roman instead of arabic. The other major difference are the big circles of the dial. This model have only one while 1815 has both as the one offered by Trevor.
Here are the 3 watches 1st, Trevor's, 2nd the 1815 ant 3rd the Richard Lange:
Regards,