Calibrating eyepiece graticule for actual microscopic measurement

Steps:

• Calibrate the eyepiece graticule using a stage micrometer at the given magnification to determine units per division.
• Focus the transverse section slide under the microscope with the ×10 eyepiece.
• Measure the xylem vessel width in eyepiece graticule units.
• Calculate actual width using the formula: actual size = (graticule units × calibration factor).

Why D is correct:

• Steps 3 and 4 directly involve measuring in graticule units and applying the calibration formula, essential for converting observed size to actual width under ×10 eyepiece magnification.

Why the others are wrong:

• A includes unnecessary steps 1 and 2, likely slide preparation irrelevant to measurement.
• B omits critical calibration and calculation (3 and 4).
• C includes extraneous step 2, such as focusing, not required for the width computation itself.

Final answer: D