9700 Paper 3 expects you to calibrate an eyepiece graticule against a stage micrometer and use it to measure cells. Line up the two scales on a virtual microscope, find what one eyepiece unit is worth, then measure cells and photomicrographs. A different objective and graticule every time.
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Lining up the graticule with the stage micrometer over a long distance, then 1 eyepiece unit = stage length ÷ eyepiece units.
Cells measured in eyepiece units, then converted with the calibration for that objective.
Actual size = image length ÷ scale-bar length × scale-bar value.
1 mm = 1000 µm and 1 µm = 1000 nm, with answers to sensible significant figures.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.