Sometimes it is difficult to determine in a micrograph if one element lies above or below another. Does the thin horizontal trail of red paint here lie over or under the black? In other words, is it a result of Mondrian's red brush grazing a black ridge after finishing the corner of the red field, or is it the trace, not fully scraped away, of an earlier position of the red block? Such questions are easier to answer when looking through the stereomicroscope itself, which preserves a three-dimensional view.