The haemocytometer is a special thick glass slide. There are four grooves on the glass slide to form three platforms. The platform in the middle is wider, and the middle is divided into two halves by a short horizontal slot. Each half is engraved with a small grid. Each grid is divided into nine large squares, with a large square in the center. For counting, it is called counting area. There are two types of scales in the counting area: one is the counting division is divided into 16 middle squares (large squares are separated by three lines), and each middle square is divided into 25 small squares; the other is a counting division There are 25 middle squares (the middle squares are separated by double lines), and each middle square is divided into 16 small squares. But no matter what kind of structure the counting area is, they all have a common feature, that is, the counting area is composed of 400 small squares. If the side length of the counting area is 1mm, the area of the counting area is 1mm2, and the area of each small square is 1/400mm2. After the cover glass is covered, the height of the counting area is 0.1mm, so the volume of each counting area is 0.1mm3, and the volume of each small square is 1/4000mm3.