Rubber trees are tapped about once every two days, yielding a cupful of latex, containing approximately 50 grams (1.7 ounces) of solid rubber, each time. The standard method of tapping is to score the tree with a knife for half the circumference of the trunk, slanting the cut down from left to right at an angle of 30° starting at the highest point convenient to the tapper. Each subsequent cut is made immediately below its predecessor. Trees are often rested for a period after heavy tapping. Production commences when a tree is 5 or 6 years old; with care, the tree’s useful life may extend to more than 20 years. With trees cultivated at a density of 375 per hectare (150 per acre), approximately 2,500 kg of rubber can be produced per hectare per year (that is, approximately one ton per acre per year).