When measuring forensic evidence, ISO regulations require that forensic laboratories document how uncertainty in the results was calculated. This article provides advice to laboratories on being comfortable with these calculations. Using trigger pull measurements as an example, three questions are asked to make sure the examiner is using the correct procedures to calculate uncertainty. The article discusses how probability measurements can reduce the uncertainty of the testing results. The authors provide an overview of the ISO requirement regarding laboratory procedures for calculating uncertainty of measurements. The authors next address the final aspect of the examination process, deciding the best way to report the results to reduce the possibility of misrepresentation. Several ethical issues regarding presentation of the findings are discussed. Figures