The science of estimating or measuring geometrical quantities such as volume, surface area, length, and numbers of objects. Examples in the biological sciences are: volume of trees in a forest, surface area of the lung, length of capillaries in a tumor, cells in an organ. The earliest applications of stereology were in ecology, forestry, and agricultural sciences. Today stereology is used in toxicological studies, marine sciences, botany, zoology, anatomy, and most other biological sciences. The importance of stereology is to provide unbiased quantification of biological structures. Commonly used stereological methods under the microscope include: the proportionator, point counting, optical fractionator, physical disector, nucleator, planar rotator, and fractionator. Macroscopic applications of stereology include prism gauges, field quadrats, point probes, and Rosiwal traverses.