Angle gauge

An angle gauge is similar to a wedge prism though it must be held a fixed distance from the eye to work properly.

Unlike the wedge prism, which is held over the plot center, the surveyor's eye is kept over plot-center when using an angle gauge.

It is multiplied by the number of trees on the plot to give basal area per acre.

The equation to calculate the limiting distance in feet is diameter at breast height, DBH, in inches times plot radius factor, PRF, in feet/area Dlim = DBH×PRF.

The PRF using a 10 BAF angle gauge is 2.75 feet (0.84 m) for every inch of tree diameter.