The Trick Flow double roller timing set is fully adjustable via the crank gear. The straight up position is marked by the "zero" on the inner radius of the gear. It must be installed aligned with the crank keyway. The outer markings are used to align with the crank gear. Note the "zero" on the outer radius of the gear. This is what you line up with the dimple on the cam gear. That is the TDC position for cylinder number six. When the crank is rotated and both marks are at the top, it is the TDC position for the number one cylinder. We used our favorite tool, the Altronics Digital Degree Wheel and a dial indicator tool in the lifter bore to degree the cam. The spec called for 104 degrees and we hit pretty close at 103.5 degrees right out of the box. If, for example you want to advance the cam, say two degrees, you would line up the A2 on the inner radius above the crank keyway and align the dimple on the cam gear with the A2 mark on the outer radius of the crank gear.