the first picture is a screenshot of the hodinkee-watch that seems to be a Mark II (the groove can be seen)
View attachment 283175
this one is a Mark I (picture copied from the web - but don't remember from where) - lugs without a groove
View attachment 283177
I believe that most Mark II have the "E" from El Primero written very close to the seconds counter register (on the left)
this is the hodinkee-watch
View attachment 283181
the next one is mine (also a Mark II with 707 serial)
View attachment 283182
and this one is a Mark 1 (picture from somehere in the web) with the E much further away from the seconds counter.
View attachment 283183
But this is just my believe. I am happy to learn if others can correct.
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