Elevation Code ElevCodeType extElevCodeType refinedElevCodeType refinedExtElevCodeType POSC 1.0 CF casing flange: A flange affixed to the top of the casing string used to attach production equipment. It is sometimes used as a reference point for wellbore measurements. CV crown valve: Also known as a swab valve. It is the uppermost valve on the vertical bore of the christmas tree above the flowing outlet, and is sometimes used as a reference point for wellbore measurements. KB kelly bushing: The point in a wellbore where the wellbore, when originally drilled, intersected the kelly bushing. RB rotary bushing: The point in a wellbore where the wellbore, when originally drilled, intersected the rotary bushing. The rotary bushing is located on the rotary table opening, and is often equivalent to the derrick floor as a basis for elevation measurements. GL ground level: The earths surface where the drillstring enters the ground. This reference point is not appropriate for an offshore well. DF derrick floor: The point where the wellbore intersects the platform, usually 10 feet or more above the ground, or the derrick on which drilling operations are carried on. RT rotary table: The point where the wellbore meets the rotary table. SF sea floor: The point in a wellbore where the wellbore intersects the sea floor. This is sometimes used as a reference point for wellbore measurements LAT lowest astronomic tide: The point in a wellbore where the wellbore intersected the surface of the sea, when the sea was at its lowest recorded level. KO Kickoff Point: The point in the parent wellbore where the sidetrack or reentry wellbore begins significant deviation from the parent wellbore. SL sea level: The point at which the wellbore intersects the mean sea level geoid. This point is generally used when sea level is used to reference wellbore measured depth measurements. UN unknown: The type of reference point is unknown.