The protocol behind every number in this part, written before the data are collected so that the data can be pooled. The tensile standard for plastics was written for moulded specimens [1], ISO/ASTM 52903-2 covers material extrusion [2], and the field still lacks agreed specimen orientation names and parameter reporting [3]. Our answer is the protocol the cohort tensile lab already uses: a fixed specimen and slicer profile, a reference series that every group prints on its own printer beside its variant, one group that prints the reference twice to measure the noise, a hypothesis written before the test, and everything about the print recorded. From such data a design value is the lower bound, the fifth percentile across printers and operators, not the mean. The chapter covers specimen design and orientation in ISO/ASTM 52921 notation, the DIC strain measurement of our machine, rejection criteria, the statistics of a two-series comparison, how the open dataset is published, and the consent and authorship questions of student data. It ends with the step from test to model: an orthotropic material calibrated on the data and checked against a printed component.