to change ropes at rebelays and are lighter. Cowstails - lanyards used to clip into safe points of contact when changing over at rebelays and while using traverse lines. They are made from a length of dynamic rope with two lanyards of differing length ending in carabiners. Knife - used as safety equipment to cut ropes, cut hair caught in descenders etc. Whistle - on long pitches where shouting is ineffective, whistles are used to signal other team members. Ladders Early cavers used rope ladders with timber rungs. These were superseded by wire 'Elektron' ladders at the start of the 1960s and remained the most common method of descending large shafts until around the end of the 1980s. Today they are largely used for descending short or tight pitches. The rungs of the ladders are usually made of aluminium tube because it is light and strong. Ladders are usually made in 5 m (15 ft), 8 m (20 ft), or 10 m (30 ft) lengths, and can be clipped together to make longer lengths. While ladders can be used without a belay, this is unsafe and is not recommended. Ladders may be carried coiled, without other protection, until needed, or may be carried inside tough PVC tackle-bags. Rope Dynamic rope, more commonly used in climbing, is used in caving for belaying cavers on climbs or using ladders. Static rope, once past its useful life for abseiling, is often used for fixed aids, such as handlines on climbs. The rope may be knotted to help climbers. Rope may also be recycled for digging. Bolting Most caves require artificial anchor points to secure abseiling rope. A common method of placing bolts is to hand drill them using a hammer and a self-drilling bolt, using bolts adapted from the construction industry. A hanger can then be screwed into the bolt. Since affordable battery drills came on the market it is more common to see cavers drill the holes and use a variety of different bolts and concrete screws. Stainless steel resin bolts are used on routes that see a lot of traffic as they have a long life and, if placed correctly, are safe and reliable. Surveying equipment Cave surveying is a specialist activity undertaken within caving to produce maps of caves. The type of equipment used depends on the intended accuracy of the survey. A basic survey may be carried out with