The haemocytometer is a thickened glass slide with small chamber of grids cut into the glass and is used to count cells. Each chamber has a fixed volume and is etched into nine large squares (see figure, P to X ), each measuring 1 ~mm 1 ~mm and 0.1 mm deep. Each large corner squares ( P , R , V and X ) contain 16 small squares. With a coverslip in place, each of these small squares represents a volume of 0.1 ~mm ^3 (