Page "Vernier scale" Paragraph 3

When a measurement is taken by mechanical means using one of the above mentioned instruments, the measure is read off a finely marked data scale ( the " fixed " scale, in the diagram ).

The measure taken will usually be between two of the smallest graduations on this scale.

The indicating scale (" vernier " in the diagram ) is used to provide an even finer additional level of precision without resorting to estimation.