David is exactly right, except the cam turns at half engine speed, not twice the same. Also, the #1 plug tower does NOT align with the contact inside the cap - take a close look inside the cap and you see the conductor from inside to outside molded inside the plastic. The proper method of aligning the distributor is to find the drilled mark on the shaft next to the gear, and the cast mark on the case, and align them, and hold that alignment as you stab the dizzy with the stud on the head aligned with the middle of the adjustment slot, allowing the shaft to turn only once it begins to engage in the gear on the cam. This initial timing must be later corrected with a timing light and the timing adjustment wire grounded at the firewall.