What information does a target cost-per-acquisition (cpa) bid strategy need in order to find the optimal cost-per-click (cpc) bid for an ad each time it's eligible to appear?

When balancing wheels with either dynamic or road force balancers, technician a says it is really important to follow the instructions provided with the particular balancer you're using. technician b says that when rebalancing a wheel, if it is out of balance, it is best to remove the old weights and recheck the balance before adding new weights. who is correct?