a device for measuring distances by means of a measuring unit and a flexible line (usually steel wire). Length gauges are used in mine surveying work.
The main components of a length gauge are a measuring unit connected to a revolution counter, and pulleys that lead the wire into the measuring unit. Devices for tightening the wire and suspending it over the line being measured are also part of the gauge. Length gauges measure horizontal and sloping distances by the number of turns of the measuring unit as it moves along the wire, which is stretched between two points. A length gauge can measure distances up to 500 m with an average error not exceeding 1:10,000. Length gauges are made for measuring the depth of vertical mine shafts (up to 1,000 m). According to their principle of operation, length gauges are analogous to the mechanical depth gauges used in navigation.