A hematometer is a device used for measuring the count of white blood cells or red blood cells in a blood sample. There are several other terms used to describe this device, including a haemocytometer, a blood cell counter, or a blood counting chamber. The term erythrocytometer is also sometimes used specifically for measuring red blood cells. Other variations include a leukocyte counter, which is used for counting white blood cells, and a Coulter counter, which uses electrical impedance to count cells. Regardless of the specific terminology used, these devices are essential tools in the diagnosis and treatment of a wide range of medical conditions.