Can an angle gauge really evaluate "borderline trees" accurately in variable plot sampling?

Detailed measurements on approximately 900 "borderline trees" verified that professional cruisers are precise in their use of wedge prisms, and that errors cancel. The fact that trees are not round gives variable plots that are not round but of the correct size. Noncancelling errors were mostly due to steep slope corrections and difficulty in seeing the tree clearly. The tree count bias was −0.5% of total cruise tree count. Reasons for checking trees are detailed. The authors recommend measuring doubtful trees with a diameter tape, for a variety of reasons, even though the bias is small.