an orienteering or diving compass and distances paced by foot or estimated. A more accurate survey would make use of a tape measure and specialist surveying compasses and inclinometers. Recently there has been a shift to wholly digital cave surveying. Measuring instruments The most common device used by cave surveyors is a sighting compass, such as that manufactured by Suunto or Silva, that can be read to the half-degree. Compasses used for cave surveying have to be rugged to cope with the harsh conditions. For high grade surveys, inclinometers are required, and are sometimes made in combined units with compasses. Recently, digital compasses and inclinometers have been developed by enthusiasts, some with wireless connections to PDAs, though these have not yet attained widespread use. Measuring distance A standard fibreglass tape measure is commonly used to measure distance, usually in lengths of . Laser rangefinders have recently gained popularity, though tapes remain preferable in especially wet or muddy conditions. Recording data Tough waterproof paper is used to record data, the advantage being that, if the paper becomes excessively muddy, it can be washed off in a stream or pool. Paperless surveying is now becoming a reality as digital measuring devices can be wirelessly connected to PDAs where the data is stored and drawn. Communication Communication between cavers and people on the surface may be essential for rescues or expeditions. Communication may be as simple as coded whistle blasts, though they are only effective across short distances and cannot be used in underwater caves. Telephones have been used in mines since at least June 1882, while the first record of telephones used in caving is from 1898. Édouard-Alfred Martel and his cousin Gabriel Gaupillat utilized lightweight telephones of with up to of wire to explore deep pitches. However, it is possible that telephones were used in Lamb Leer caverns before February 1885, as there are references to a "talking machine" in use before this time. Radio communication within caves is problematic because rock is a conductor and therefore absorbs radio waves. Ordinary radios have a very short range within caves. Low frequency (LF) or very low frequency (VLF) radio with single-sideband modulation is more commonly used today. Early models were called "speleophones". See also Flashlight References External links Cave-link Home Page HeyPhone Home Page