The proportionator is a method of cell counting that employs PPS, probability proportional to size. Although, the method utilizes sampling that is not uniform, i.e. every cell having the same chance of being selected, the method remains unbiased. The proportionator becomes more efficient than earlier counting method when the distribution of cells is less uniform. The more variance experienced in counting, the more efficient the proportionator becomes. Earlier unbiased counting methods include the optical fractionator, physical disector, and empirical method. Outdated and biased methods include the Abercrombie method, Floderus method, Rose-Rohrlich unfolding method, and raw cell profile counting method.