Chinese plucked board zither roughly 47 inches (120 cm) long and 12 inches (30 cm) wide. Its resonator is galley-shaped, and in cross section the top is curved and the bottom flat. The strings are stretched over the surface, fastened at the left end and at the right where there are pegs for tuning. A moveable bridge under each of the strings can adjust the string's pitch. In different historical periods, the number of the strings varied: in roughly the 5th century, there were 12 strings, from the 10th to the 14th century, 13 strings, and from the 14th century on, 15 or 16 strings. In the 1960s the number increased to 18, 21, and 25 strings. The most frequently used type has 21 strings. Present-day strings are metal, although they were probably silk in ancient times. In performance the zheng is placed on a table or rack in front of the player, who plucks the strings to the right of the bridges using the first three or four fingers of the right hand. Ornamentations and pitch alterations are created by pressing on the strings to the left of the bridges with the fingers of the left hand.