FIGURE 44.

Measuring section thickness. Section thickness, t, can only be measured with a precision to within twice the depth of field (DoF, red boxes) of the objective that is used to make the measurement. Depending on the perception of focus, it may be overestimated (early recognition) or underestimated (late recognition) by the depth of field of the focal plane. Variations in top and bottom focal plane positions within the field of view but outside the actual sampling site require top and bottom focal plane positions to be found at the sampling site [Color figure can be viewed at wileyonlinelibrary.com]