The main measuring element of the glass tube rotameter is a vertically mounted conical glass tube and a float that can move up and down inside. When the fluid from the bottom up through the conical glass tube, in the float between the upper and lower pressure difference, the float in this differential pressure under the action of rising. When the rising force, the buoyancy force and viscous force on the float is equal to the gravity of the float, the float is in equilibrium position. Therefore, the flow of fluid through the glass rotameter and the float rise height. That is, there is a certain proportional relationship between the flow area and the glass rotor flowmeter. The float position height can be used as a measure of flow.