Foresters usually measure the diameter of trees at Breast Height – traditionally 4 foot, 6 inches – now 1.3 m – which is termed Diameter Breast Height Over Bark (DBHOB). Basal Area is the cross section of the tree trunk at breast height, and the sum for the stand or group of trees is expressed square feet per acre (after 1973 it was expressed in square metres per hectare). Lots of skinny trees, or a few fat ones, can have the same Basal Area, but when combined with the number of stems, Basal Area is a good indicator of stand density. Two common methods are used to measure of Basal Area – fixed area plots and angle count sampling. 1. Fixed area plots require setting out a small area, commonly 50 m x 20 m, and measuring all the trees at breast height, and doing some quick sums. 2. Angle count sampling involves a simple sweep of the forest from a fixed sampling point using a relascope, dendrometer sight, angle gauge, or glass wedge prism. This wooden builders ruler has been shaped at one end to create a shallow angle (usually less than 3 degrees). Standing in one spot, a sweep is made with the wedge held to the eye, and trees are counted as either “in” or “out”. The number of trees is multiplied by conversion factor of the wedge (10 in this case) to estimate basal area. It’s very quick and effective.Basal Area Angle Gauge The two ends fold up and one end (on the right) has been reduced in width to create a shallow angle for the viewer Home made by cutting down a wooden builder's ruler Many forestry students made their own Basal Area Angle Gauges and its thought this may be oneforest measurement, forests commission victoria (fcv)