Handling borderline trees: counts all tree stems not completely offset when viewed through the wedge; others are not tallied. Trees that appear to be borderline should be measured and checked with the appropriate plot radius factor before arbitrarily deciding to tally every other borderline stem. Dimension: 40 mm X 40 mm Accurate to ± 1% of rated BAF. Efficient familiar design (30° ellipse curvature at top). Base is parallel to horizontal axis for slope correction reference. Leather case.