Borehole logging, also known as well logging is the detailed recording of the in situ ground conditions encountered in a borehole. The required information result from visual inspection of samples brought to the surface or from geophysical measurements along the axis of a borehole carried out with a special logging device that is lowered into the hole. This device is manipulated up and down the borehole recording geotechnical data. Borehole tools range from mechanical devices, nuclear/gamma, acoustical, electrical, imaging, and sensors for fluid properties. Data acquired are usually documented in a standardized log spreadsheet.