Unknown wheel… ETA 900 15 Jewel movement

[PRLJAMR]

Any help in identifying this wheel?  I’m not sure of its purpose or how it’s held onto the movement?  I can’t find any other caliber 900 ETA’s with the same configuration.  I’m fairly new to the hobby so please forgive me if this is a ridiculous question. Appreciate any suggestions.  

[LittleWatchShop]

Sweep second wheel as shown here

[PRLJAMR]

3 hours ago, LittleWatchShop said:

Sweep second wheel as shown here

Exactly what I was looking for!  Thank you!  

[Klassiker]

An interesting but sadly not well presented pair of articles explaining the contortions performed to display the seconds on the same axis as hours and minutes.

https://www.timezone.com/2002/09/24/the-pursuit-of-center-seconds-part-1/

https://www.timezone.com/2002/09/24/the-pursuit-of-center-seconds-part-2/

[PRLJAMR]

18 hours ago, Klassiker said:

An interesting but sadly not well presented pair of articles explaining the contortions performed to display the seconds on the same axis as hours and minutes.

https://www.timezone.com/2002/09/24/the-pursuit-of-center-seconds-part-1/

https://www.timezone.com/2002/09/24/the-pursuit-of-center-seconds-part-2/

Very interesting article.  Thank you for sharing!