1. Walstrom , J. E. Brown , A. A. Harvey , R. P. An Analysis of Uncertainty in Directional Surveying Journal of Petroleum Technology April 1969
2. Wolff , C. J. DeWardt , J. P. Borehole Position Uncertainty. Analysis of Measuring Methods and Derivation of Systematic Error Model SPE Paper 9223, 55th Annual Conference, Society of Petroleum Engineers September 1980
3. Marsh , J. L. Hand-Held Calculator Assists in Directional Drilling Control Petroleum Engineer International September 1982
4. Guillory , C. Surface Recording Gyroscope System Saves Rig Time The Oil and Gas Journal May 8, 1978
5. Warren , T. Directional Control and Target Location SPE Forum on Well Blowout Control, Glenwood Springs, CO. August 1980