The beating heart of the watch, we adopted the CITIZEN MIYOTA-made Cal.9039, a Japanese–manufactured high beat movement.

This high beat movement oscillates 28,800 times per hour (8 times a second), reducing the distance of the swing of the second hand and drastically increasing the precision of the watch.
The thickness of the Cal.9039—a mechanical movement that MIYOTA revived after a period of around 30 years as a thin-type high performance 8-beat movement—is a mere 3.9mm, unrivalled even by the Swiss-made ETA2824, which gained worldwide popularity.

 
Please see the below for more details:
https://miyotamovement.com/product/9039/