Volumetric pipettes or bulb pipette allow the user to measure a volume of solution extremely precisely (precision of four significant figures). These pipettes have a large bulb with a long narrow portion above with a single graduation mark as it is calibrated for a single volume (like a volumetric flask). Typical volumes are 20, 50, and 100 mL. Volumetric pipettes are commonly used to make laboratory solutions from a base stock as well as prepare solutions for titration. Graduated pipettes Main article: Graduated pipette Graduated pipettes are a type of macropipette consisting of a long tube with a series of graduations, as on a graduated cylinder or burette, to indicate different calibrated volumes. They also require a source of vacuum; in the early days of chemistry and biology, the mouth was used. The safety regulations included the statement: "Never pipette by mouth KCN, NH3, strong acids, bases and mercury salts". Some pipettes were manufactured with two bubbles between the mouth piece and the solution level line, to protect the chemist from accidental swallowing of the solution.