The first is locking and unlocking the escape https://is.gd/QrzXfV link wheel. Keep in mind that this only happens at the precise moment the balance makes it happen. That means that as long as the balance is swinging at the same rate, the gear train advances at extremely regular intervals. https://zzb.bz/9G3itJ link Put https://zzb.bz/UeBAhg link some hands on wheels further back in the gear train to show when the gear train unlocks, and you've got a watch.