Hemacytometers were the first tools used to perform manual cell counts. A standard ‘charge’ would fill a 3×3 gridded area which was eactly 0.9uL. The coulter counter was one of the first automated laboratory instruments and would count using a tube so skinny exactly one cell could fit through its diameter. A constant electrical charge would be flowing across a part of the cross section and the charge would be impeded by a cell traveling through through. The resistance was measured and directly correlated to cellular volume.
MCHC = HGB * 100 / HCT
MCH = HGB *10 / RBC
MCV = HCT * 10 / RBC