Refers to the mathematical methods and assumptions used in reconstructing the path of the wellbore and in generating the space curve path of the wellbore from inclination and direction angle measurements taken along the wellbore. These measurements are obtained from gyroscopic or magnetic instruments of either the single-shot or multi-shot type. Acceleration Method: Utilizes the angles at the top and bottom of the course length and from these generates a curve on the assumption that the measured angles change smoothly from top to bottom of the measured course as though under the influence of a constant force of an acceleration. The results obtained are the same as “Balanced Tangential,” “Trapezoidal,” and Vector Averaging” Methods. Average Angle Method: Uses the angles measured at both the top and bottom of the course length in such a fashion that the average of the two sets of measured angles is the assumed inclination and direction. The well bore survey is then calculated tangentially using these averaged angles over the course length. Angle Averaging Method: Refer to “Average Angle Method”. Backward Station Method: Refer to “Tangential Method”. Balanced Tangential Method: Uses the inclination and direction angles at the top and bottom of the course length in a manner so as to tangentially balance the two sets of measured angles over the course length. Results obtained are the same as the “Acceleration,” “Trapezoidal,” and Vector Averaging” Methods. Circular Arc Method: Uses both sets of measured angles associated with each course length to recreate the wellbore path as a sequence of small circular arcs constrained by the measured angles to pass through the end points with inclination and direction angles as measured. Compensated Acceleration Method: Refer to “Mercury Method”. Combined Method: Refer to “Mercury Method”. Mercury Method: A combination of the “Tangential” and “Balanced Tangential” Methods so as to treat that portion of the measured course defined by the length of the measuring tool as a straight line (tangentially) and the remainder of the measured course trapezoidally. Refer to “Compensated Acceleration Method” and “Combined Method”. Minimum Curvature Method: Uses the sets of angles measured at the top and bottom of the course length to establish coordinate velocities through which a space curve (which represents the calculated path of the wellbore) passes in a manner that minimizes its total curvature. Quadratic Method: A method in math modeling considering the wellbore as a curve; the projections into three orthogonal planes are quadratic functions. Radius of Curvature Method: Uses the sets of angles measured at the top and bottom of the course length to generate a space curve (representing the wellbore path) that has the shape of a spherical arc passing through the measured angles at both the upper and lower ends of the measured course. Secant Method: This name has been applied with two different meanings: (1) meaning the “Trapezoidal Method,” and (2) meaning the “Average Angle Method”. Simpson’s Rule Method: Uses as many measured angle values as are available (a minimum of three sets) to recreate the wellbore path through Simpson’s Rule for numeric integration, which approximates by passing a parabola through three points. Tangential Method: Uses only the inclination and direction angles measured at the lower end of the course length. The wellbore path is assumed to be tangent to these angles through the course. Terminal Angle Method: Refer to “Tangential Method”. Trapezoidal Method: Uses the measured inclination and direction angles at both ends of the measured course in a fashion that recreates the wellbore path. This is done by a sequence of trapezoidal integration segments using the measured angles as constraints on the integral over the measured course. Results obtained are essentially the same as “Acceleration,” “Balanced Tangential,” and “Vector Averaging” Methods. Vector Averaging Method: Uses inclination and direction measurements at both ends of the measured course to establish vector space direction. It is then assumed that each of these two vectors is projected for one-half the course length in creating the wellbore path. Each “half course length” segment can be treated tangentially. Results obtained are essentially the same as the “Acceleration, “Balanced Tangential,” and “Trapezoidal” Methods. (Bul D20)