The girth of a tree is usually much easier to measure than the height, as it is a simple matter of stretching a tape round the trunk, and pulling it taut to find the circumference. Despite this, UK tree author Alan Mitchell made the following comment about measurements of yew trees: The aberrations of past measurements of yews are beyond belief. For example, the tree at Tisbury has a well-defined, clean, if irregular bole at least 1.5 m long. It has been found to have a girth that dilated and shrunk in the following way: 11.28 m (1834 Loudon), 9.3 m (1892 Lowe), 10.67 m (1903 Elwes and Henry), 9.0 m (1924 E. Swanton), 9.45 m (1959 Mitchell) ... Earlier measurements have therefore been omitted. As a general standard, tree girth is taken at "breast height". This is cited as dbh (diameter at breast height) in tree and forestry literature.[10][11] Breast height is defined differently in different situations, with most forestry measurements taking girth at 1.3 m above ground,[11] while those who measure ornamental trees usually measure at 1.5 m above ground;[10] in most cases this makes little difference to the measured girth. On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk,[10][11] but in North America a point, that is the average of the highest point and the lowest point the tree trunk appears to contact the soil, is usually used.[12] Some of the inflated old measurements may have been taken at ground level. Some past exaggerated measurements also result from measuring the complete next-to-bark measurement, pushing the tape in and out over every crevice and buttress.[13] Modern trends are to cite the tree's diameter rather than the circumference. Diameter of the tree is calculated by finding the medium diameter of the trunk, in most cases obtained by dividing the measured circumference by ?; this assumes the trunk is mostly circular in cross-section (an oval or irregular cross-section would result in a mean diameter slightly greater than the assumed circle). Accurately measuring circum erence or diameter is difficult in species with the large buttresses that are especially characteristic in many species of rainforest trees. Simple measurement of circumference of such trees can be misleading when the circumference includes much empty space between buttresses. One further problem with measuring baobabs Adansonia is that these trees store large amounts of water in the very soft wood in their trunks. This leads to marked variation in their girth over the year (though not more than about 2.5%[14]), swelling to a maximum at the end of the rainy season, minimum at the end of the dry season. The stoutest living single-trunk species in diameter are: Montezuma Cypress Taxodium mucronatum: 11.62 m (38.1 ft), Arbol del Tule, Santa Maria del Tule, Oaxaca, Mexico.[15] Note though that this diameter includes buttressing; the actual idealised diameter of the area of its wood is 9.38 m (30.8 ft).[15] Giant Sequoia Sequoiadendron giganteum: 8.85 m (29.0 ft), General Grant tree, General Grant Grove, California, United States[16] Coast Redwood Sequoia sempervirens: 7.9 m (26 ft), Lost Monarch Jedediah Smith Redwoods State Park, California, United States. Australian Oak Eucalyptus obliqua: 6.72 m (22.0 ft) Australian Mountain Ash Eucalyptus regnans: 6.52 m (21.4 ft), Big Foot Western Redcedar Thuja plicata: 5.99 m (19.7 ft), Kalaloch Cedar, Olympic National Park Sitka Spruce Picea sitchensis: 5.39 m (17.7 ft), Quinalt Lake Spruce, Olympic National Park Kauri Agathis australis: 5.33 m (17.5 ft), Te Matua Ngahere, Waipoua Forest, New Zealand[17] An additional problem lies in instances where multiple trunks (whether from an individual tree or multiple trees) grow together. The Sacred Fig is a notable example of this, forming additional "trunks" by growing adventitious roots down from the branches, which then thicken up when the root reaches the ground to form new trunks; a single Sacred Fig tree can have hundreds of such trunks.[18] The multi-stemmed Hundred Horse Chestnut was known to have a circumference of 57.9 m (190 ft) when it was measured in 1780.