Its the crystal. It has 3 steps towards 3 and 9. When it came out, I was presented with a box of all the individual components of the watch and suffice to say, the optical ilusion they are able to achieve with that saphire machining is nothing short of miraculous.
Also the full name logo bellow the 12th index is held just on 2 tiny pins and its applied by hand. So the error rate and scrap rate of the dials at the very beginning was astronomical. One tiny slip-up by the watchmaker and the dial, that takes over 16hrs to paint and bake to the mirror finish is ruined.
Its really a very interesting line. i was weary of the first batch, but then they came out with the funky colours and now they are doing very interesting complications, like the chimes, wondering hours, etc. My favourite was the aventurine perpetual from the first year, but not anymore lol
EDIT:
here its visible