The 2 courses are Course A and Course B. Class A pipettes are made to exact tolerances, or "mistake restrictions". Class B are authorized twice the mistake limitations of Course A. The class specification or serial amount of Class B are usually not marked. Pasteur pipettes with rubber bulbs connected. https://laboratory-pipette-types34444.shoutmyblog.com/28933985/top-types-of-pipette-ppt-secrets