Complex sentence: The annual rings in the planks that are cut as the saw moves toward or away from the center of the log are short arcs that approach the faces at increasingly steeper angles, while the center planks have annual rings that are nearly perpendicular to the faces.
Split into simpler sentences: The annual rings in the planks that are cut as you move toward or away from the center of the log are short arcs that approach the faces at increasingly steeper angles. While the center planks have annual rings that are nearly perpendicular to the faces.