Time to watch
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The 1815 is a superb watch, you can’t go wrong with either.
Personally my choice was and is the 5170

The reasoning for me was the following.
It’s a historic achievement for Patek, the first fully in-house manual chrono.
Also I find Langes in general to be a bit top heavy when worn, something I am not comfortable with.
The 5170 is a manual watch that you cannot overwind, pretty cool in my opinion.
The variation of dials within the 5170 range means each has its own distinct character. Something for everyone.
I’d Ike to add that I haven’t had any issues with my watch.
Again, you won’t be wrong choosing either. They’re both fantastic watches.