The Cell Counting Z1 Single and Dual Threshold Models use the Coulter Principle (Electrical Sensing Zone Method) for counting cells or particles in the 1120 micron size range. This technique offers accuracy, speed, versatility, and excellent precision. Standard apertures are available in five different sizes. Ampoule insertable apertures may be used for very small sample volumes. The Z1 Single Threshold instrument allows the operator to set one size threshold. It then counts the cells equal to or larger than this setting. It is ideal for the rapid enumeration of both tissue culture and blood cells from most species. It is excellent for rapid total cell count on cell lines containing cells of relatively uniform size. The Z1 Dual Threshold Model counts cells or particles in three regions, which can be equal to or above the selected size.