Two scientists are cutting samples of leaves for analysis. One scientist always clips a sample from the base of the leaf near the stem, and the other scientist always clips a sample from the tip of the leaf. This illustrates a

The scientists use different procedures to choose where to cut each leaf sample: one takes tissue near the base, while the other takes it from the tip. This can make their samples differ for reasons unrelated to the analysis, so it is a procedural error. Calibration and unit errors involve equipment settings or units, and a measurement error is an inaccurate reading.

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