The engagement of the oscillating pinion on the ETA 7750 is a topic of its own because it has a clutch mechanism for the chronograph that is not widely used in other calibers. Engagement of this wheel and pinion does not follow the normal rules for wheel and pinion engagement. Because its construction follows a different pattern than traditional horizontal clutch mechanisms, it is not possible for the teeth to make contact on the pitch circles. Proper engagement of the oscillating pinion and seconds counter wheel ensures smooth operation of the chronograph without excessive loss of amplitude or disengagement during shocks. As with all wheel engagements, the depth of engagement is measured on the line of centers (the imaginary line connecting the center of the arbors of both wheels). The teeth of the oscillating pinion should penetrate two-thirds of the depth of the teeth on the seconds counter wheel (chronograph wheel). This must be checked for all teeth on the chronograph wheel with the chronograph running and with tension on the clutch lever to accommodate for sideshake of the wheels and manufacturing tolerances. The apex of the pinion tooth should align with the transition between the dedendum and addendum of the teeth of the seconds counter wheel. The arm of the clutch lever should rest firmly against the eccentric for adjusting its depth.