The reflected energy is recorded by groups of geophones laid on the ground at equally spaced intervals (50 or 100 metres apart) along a line; the number of groups used to record each shot may be 24, 48, or as high as 96 and hence the spread length with 50 metre spacing between geophone groups varies from 1,200 metres to 4,800 metres. The ground movements resulting from the energy released by the shot cause the geophones to generate small electrical impulses which are taken by cable to a conveniently located recording station where the impulses from each of the groups are amplified and recorded in digital form on magnetic tape. ) A monitor record on photographic paper is also taken to check that a satisfactory record is obtained. The shot-point can be located either at the center of the spread or at one end of the spread. Continuous single cover subsurface data from the reflecting horizons are obtained from the spread.