Context: In the tree a knot is either the base of a side branch or a dormant bud. A knot (when the base of a side branch) is conical in shape (hence the roughly circular cross-section) with the inner tip at the point in stem diameter at which the plant's vascular cambium was located when the branch formed as a bud.

Question: Other than the base of a side branch, what tree feature causes a knot?
Answer: a dormant bud

Question: What shape is the knot formed by a side branch's base?
Answer: conical

Question: What measurement of a stem determines a knot's inner tip placement?
Answer: diameter

Question: Because a knot's shape is conical, what shape does a cross-section of it have?
Answer: circular