Calculating actual microscopic dimensions using magnification

Steps:

• Focus the transverse section under the ×10 eyepiece for clear view of xylem vessel.
• Calibrate eyepiece graticule if needed, but proceed to direct measurement for this query.
• Measure vessel width in eyepiece graticule units across the field of view.
• Divide measured units by total magnification (eyepiece × objective) to get actual width in micrometers.

Why D is correct:

• Actual size formula is actual width = image width / total magnification, requiring step 3 (image measurement via graticule) and step 4 (division by magnification including ×10 eyepiece).

Why the others are wrong:

• A includes extraneous steps 1 and 2 (e.g., drawing or setup not essential for calculation).
• B omits measurement and uses only preliminary steps, yielding no actual size.
• C skips direct graticule measurement, relying on irrelevant step 2 (e.g., calibration alone).

Final answer: D