Good Laboratory Pipetting Guide

There are two types of pipettes: air displacement and positive displacement pipettes. Air displacement pipettes are meant for general use with aqueous solutions. Positive displacement pipettes are used for highly viscous and volatile liquids. Both pipette types have a piston that moves in a cylinder or capillary. In air displacement pipettes, a certain  volume of air remains between the piston and the liquid. In positive displacement pipetting, the piston is in direct contact with the liquid.

Open the guide here:
guide-to-pipetting-2.pdf

Source: Thermo Fisher
Image credits: Wytamma Wirth‎