Final answer:
To log a retest sample, the sample identification number must be entered after checking the retest box.
Step-by-step explanation:
To log a retest sample on an equipment item, after checking the retest box, you need to enter the sample identification number in the attached box. This is essential because the sample identification number is what uniquely identifies the specific sample that is being retested, linking it back to the original test and ensuring accurate tracking of test results and quality control procedures.