Air displacement pipettes and positive displacement pipettes are two types of laboratory pipettes that are used to measure and dispense small volumes of liquid. Air displacement pipettes, also known as air-jet or jet pipettes, work by creating a stream of air that is used to aspirate liquid into the pipette. The user sets the volume to be dispensed by adjusting the position of the pipette's tip within the pipette's barrel. The user then pushes the pipette's plunger to dispense the liquid. The volume of liquid that is dispensed is determined by the position of the plunger and the size of the pipette's tip. Positive displacement pipettes, on the other hand, work by physically trapping a specific volume of liquid within the pipette's tip. The user sets the volume to be dispensed by adjusting the position of the pipette's plunger, and then pushes the plunger to dispense the liquid. The volume of liquid that is dispensed is determined by the volume of the pipette's tip and the position of the plunger. Positive displacement pipettes are commonly used for dispensing viscous liquids, such as oils and suspensions. In general, positive displacement pipettes are more accurate and precise than air displacement pipettes, but they are also more expensive and can be more difficult to use. For this reason, air displacement pipettes are often used for routine tasks that do not require high levels of accuracy and precision, while positive displacement pipettes are used for more critical applications. While air displacement pipettes use air to measure the volume, positive displacement pipettes do not use air. Instead, they use the shape of the tip, the movement of the piston, and the properties of the liquid to dispense a specific volume.