Counting Reticle, Chalkley 25 Dots

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This is used to determine the relationship of components to each other quickly by using random sampling. An example of its application is given by Curtis, where a researcher might want to see whether or not a certain drug affects the volume proportion of cell types in a given organ. With this graticule the proportion of points lying over the image of one type of component is statistically proportional to the area occupied by that component. The 25 points of the array are placed over the field of view at random, so that a comparison can be made between the number of points touching the one type of component in each viewing, with the number touching the other type of component. A series of observations will yield art increasingly accurate ratio of the comparative incidence of each type of particle.

Ref. A. S. C. Curtis, Medical and Biological illustration, volume 10, pp. 261-266. 'Area and volume measurements by random sampling methods'.


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