The watch world can be quite strange at times:
Patek is releasing another chrono in many years and is using a supplier for the movement instead of developing one own movement.
However it becomes a big success, possibly a bigger one than Patek was expecting.
I could imagine the reason for this big success is the wider use of the internet from 1998 onwards on that helped watchfans to become more aware of watches and Pateks in particular.
As the headline is saying: the 5070 is a fully functional chrono as its scaling is correct and shows 1/5 of a second on the dial, which is coherent to its beat ratio of 18.000 A/h.
Despite the success the movement was always a de-Lema-nia (pun intended) for Patek as not inhouse.
The movement of the 5170 was possibly born out of the necessity that the Swatch Group has also taken over Lemania in the Breguet deal in 1999.
I strongly believe that the contract to supply Patek with movements was undermined by the Swatch Group and hence Patek had to develop their own movement.
But this investment into an own chrono movement was well funded by the big success of the 5070, I suppose.
However, the 5170 (most likely, imho) was/is not such a big success like the 5070 which is a big, big shame as it is a genuine Patek due to its inhouse movement.
One aspect is still disappointing: the 5170 is less functional as the scaling is also showing 1/5 of a second instead of 1/8 th.
Patek could have got around this by showing four sub second marks on the scaling but in this question Patek went for the look only and chose the (wrong) classic scaling only to make it look like a classic chrono.
I do not know.
To me the 5170, albeit looking a bit bloated due to the very slim bezel, would be clearly my choice if it would also be scaled correctly.
Finally: thank you for the great post!
Cordially
Moritz