obtained from a horner plot are the initial shut in pressure and final shut in pressure and instantaneous values of pressure the horner plot is typically compiled by graphing the data the preferred presentation of the horner plot utilizes semilog paper where the abscissa is the log scale is t dt 1 dt while pressure p is the linear scale or the ordinate ideally a straight line is projected in the case of the uniform reservoir with a single fluid drive curve projection can be made so that the curve end corresponds to the passage of an infinite interval which provides fluid pressure measurement at the intercept as will be understood this intercept is represented by plotting measurements on a semilog plot to thereby represent the intercept as a useful variable in practice of the present invention the intercept is represented by the symbol b a pretest sequence occurring at a time t is defined the pretest flow rate is given by the symbol q and is measured in cc sec the incremental time after the shut in filling the drawdown chamber 90 is represented by dt this enables a first equation to be defined namely equation 1 which in turn leads to equations 2 and 3 equ1 in equation 3 above formation or zone thickness is represented by h and is measured in feet formation fluid viscosity in centipoise is represented by u03bc the slope of the.