Basic surveying was probably undertaken from the time that miners started working underground, often by the miners themselves.
It became the job of the surveyor to supervise the layout of the mine, fix the mine boundaries, map the directions new tunnels were following, and calculate the amounts and positions of ore mined.
There are records of mine surveys in Britain from the 15th century, and by the 18th century surveying was well established.
In Cornwall, the instrument most widely used to measure the mine boundaries was the dial. This is a compass especially made for use underground.
When using a dial a fixed reference point was created (often using a plumb line fixed in the mineshaft). From this starting point a line is drawn to a second point along the tunnel being surveyed. The axis of the dial was laid parallel to this line and the compass bearing noted. The distance between the two points was also measured. The line would then be extended from the second point to a third, further along the tunnel, and the dial again used to measure the bearing. In this way the direction and length of the tunnel was measured.
However, the compass was often inaccurate, as the compass needle was easily deflected by iron tools or deposits of iron in the mine.
By the middle of the 19th century more sophisticated dials were being made. These 'theodolites' incorporated telescopes, bubble levels and vertical quadrants so that vertical angles could be measured. Theodolites made surveying more accurate by 'traversing', measuring fixed points in the mine without relying upon compass bearings. By the end of the 19th century the theodolite replaced the dial as the main tool of the mine surveyor.
Today mine surveying is an exact science, modern theodolites using laser sighting and electronic storage data, coupled with GPS, offer an accuracy only dreamt of by the early surveyor with his simple dial and measuring chain.
Most mines in Cornwall employed at least one surveyor, who kept a record of all survey work and used this to draw accurate plans of the mine workings.
How modern surveying works
On the surface a surveyor takes angular and linear measurements of particular parts of the earth's surface to work out his co-ordinates. This information is plotted on a plan.
In order to work out where the underground workings are in relation to the surface, co-ordinates on the surface are transferred underground via shafts using survey instruments such as theodolites or more modern laser equipment.
Using these underground coordinates, surveyors are able to produce working plans of the mines for use in efficient day-to-day mine production and ensure safe working conditions fro the men.