The well seismic recording is a checkshot service which provides a depth-vs.-time calibration for the seismic reflection technique. Seismic velocities are measured at the well by recording the time required for a wavelet generated by a surface energy source to reach the geophones in a tool anchored in the well. The recorded travel times of the direct arrival are used to calibrate the sonic log, which then becomes the basic seismic reference and allows a surface seismic cross section to be scaled to depth.