The adjustable stopcock lets the analyst release liquid slowly drop by drop into a flask. Meanwhile, a printed column of graduated volume markings shows exactly how much liquid was dispensed. The total volume delivered is calculated by subtracting the initial reading from the final reading.
Therefore, the buret does not need to be filled to an exact zero starting mark. You must always take these volume readings with your eyes perfectly level with the liquid. The liquid surface forms a curved shape inside the glass tube called a meniscus.
You should read the measurement at the lowest point of this curved meniscus. For very dark or opaque solutions, you read from the top of the liquid instead. Analysts estimate readings to one decimal place past the printed marks, usually to 0.01 milliliters.
This exceptional volumetric precision makes the buret an absolutely essential tool for quantitative chemical analysis. It is used extensively for determining unknown sample concentrations during acid-base and redox titration experiments. Proper cleaning and preparation are necessary to prevent contamination and ensure perfectly accurate volume measurements.
Chemists must rinse the buret with the titrant solution before using it to remove water. Any leftover water would dilute the titrant and completely ruin the final concentration calculation.