Bloodstain pattern analysis employed by forensic scientists is capable of estimating the position of the source of blood spatter patterns, yet the precision of these estimations lack scientific definition. The current article explores a paper by Carter and Podworny in which the authors describe a procedure for calculating the horizontal planar position of the source of blood spatter as a point. Elementary calculus is applied to equivalent expressions of those of Carter and Podworny, allowing for the calculation of quotable uncertainties or errors. The uncertainties may vary with distance and with angular position in regards to selected stains. The final analysis indicates that careful selection of both stain integrity and the horizontal separation between stains and their position can lead to good specification for the source position coordinates. Figures, references