One of the biggest advantages of plug flow reactors lies in their narrow residence time distribution. The pulse experiment, as a common method on acquiring that distribution, relies on the tracer injection being a perfect pulse. A deviation from a perfect pulse leads to erroneous results if not taken into account. With a numerical analysis of experimental data, this effect is quantified in turbulent and laminar flow regime and the results are compared to an analytical method. Significant deviations occur mostly in the turbulent regime, which has the greatest technical relevance.