An Evaluation of the McClure and Wheeler Optical Calipers

Five trees of each of four species were measured at six positions on the bole ranging from 0.5 to 32.5 feet above ground with the McClure optical caliper's, Wheeler optical calipers, diameter tape and conventional calipers. Measurements are quickly and easily made with the optical calipers. The only statistically significant difference occurred at the three middle positions where the McClure measurements were larger than the other instruments'. The exact cause for this is not known but it is attributed to the 0.5-inch scale markings on the McClure requiring interpolation to read to 0.1 inch, as there were no significant differences between the instruments when all positions were combined in a single analysis.