A limit recorder of the intensity of ground vibrations initiated by a quarry or opencast blast. It consists essentially of a level glass base on which a number of pins 1/4 in (0.64 cm) in diameter and of lengths ranging from 6 to 15 in (15 to 38 cm) are stood upright. The pins stand inside hollow steel rods so that each pin can fall over independently of the others. The longer the pin, the less energy required to topple it. In practice it has been accepted that if the shorter pins (up to 10 in or 25 cm) remain standing, then there is no possibility of structural damage to a building by a quarry blast.