The difference in annual ring width is due to standing on a sloping ground.
By trying to stand vertically against the center of the earth, a width is born in the annual ring.
So I put a horizontal instrument in the middle of the annual ring.
You can think of the space in which this tree grew, looking at the rings.
YEAR: 2018 Dec.
MATERIAL: solid wood / Level
SIZE: H 110 x W 110 mm