The measurements given in this book are only approximate. Girth, or circumference, is given in feet and inches (veteran pre-metric tape measure!) One foot is twelve inches and converts to 30 centimetres, three feet make a yard which is approximately one metre.
Girth should be measured at chest height, 5 feet or 1.3 metres. This is easier said than done with trees which are leaning, surrounded by undergrowth, with low side branches, or growing against a wall. A few inches up or down can make a considerable difference in the circumference measurement. The tape measure must be kept level.
Height may be estimated by triangulation – in an isosceles triangle with a right angle (90 degrees) the two sides are of equal length. A stick is held with outstretched arm at eye level to form this right angle. The length of the stick must be equal to the distance between the eye and outstretched fingers i.e. are specific to each person.
The tree surveyor walks back until top and bottom of the stick coincide with tip and base of tree. The distance between that position and the tree then equals the height of the tree: this may be measured or paced out.