A common method in industry to correct pressure build-up data for producing time effects is use of Agarwal equivalent drawdown time (SPE 9289). But how does this correction affect the presentation of data and interpretation when performing well test analysis? It can be argued that a reasonable pressure match to a particular reservoir model can be achieved regardless of how the data is presented. An appropriate match can be quantified by goodness of fit criteria and the best match (model) selected on that basis. Because of the presence of non-unique solutions, it is difficult to know which flow geometry is most appropriate from the match alone. Future flow predictions will be effected by the selection an appropriate model with late time boundary conditions having the largest effect on forecasted volumes. The method presented in this paper will try to reduce the uncertainty when selecting a model to match the pressure behavior plus demonstrate that the Agarwal corrected and Horner corrected derivative are identical.