Ball SpringLOCK is a patented shock protection device that acts as a cage around the hairspring, protecting it from jolts and impacts.
According to Ball, vibrations and shocks can account for a loss of up to 60 seconds per day for a mechanical watch movement. SpringLOCK is claimed to reduce this deviation in accuracy by up to 66%.
In Ball Watch Company’s own words:
“Disorient of balance-spring upon shock impact is the most common cause of watch inaccuracy. SpringLOCK®, the world’s first revolutionary and BALL’s patented anti-shock system, enhances watch accuracy by reducing balance-spring’s shock impact by 66%.”
Ball Calibers with SpringLOCK:
We have found movements featuring this technology with the letters -CSL after the caliber number. The C is for chronometer, SL is for SpringLOCK. Not sure if they have simply -SL movements without the C (comment below if you know more about this), but since this device is supposed to improve accuracy, it makes sense that it is used in the chronometer grade movements.