Editing Vernier scale (section)

{{short description|Auxiliary scale of a measurement device, used to increase precision}}
[[File:Close up of vernier scale.jpg|thumb|right|upright=1.35|Vernier caliper scales; main at top, vernier at bottom. It reads 3.58&nbsp;±&nbsp;0.02&nbsp;mm by adding 3.00&nbsp;mm (left red mark) on the fixed main scale to vernier 0.58&nbsp;mm (right red mark). The main scale reading is that  to the left of the zero on the vernier scale. The vernier reading is found by locating the best aligned lines between the two scales. The 0.02&nbsp;mm engraving indicates the caliper's readability and is the "vernier constant" for this scale.]]

A '''vernier scale''' ({{IPAc-en|ˈ|v|əːr|n|iː|ər}} {{respell|VUR|nee|ər}}), named after [[Pierre Vernier]], is a visual aid to take an accurate measurement reading between two [[graduation (scale)|graduation]] markings on a linear scale by using mechanical [[interpolation]], which increases [[Accuracy and precision|resolution]] and reduces [[measurement uncertainty]] by using [[vernier acuity]]. It may be found on many types of instrument [[length measurement|measuring length]] or [[angle measurement|measuring angles]], but in particular on a [[vernier caliper]], which measures lengths of [[Orders_of_magnitude_(length)#1_decimeter|human-scale]] objects (including internal and external diameters). 

The vernier is a subsidiary scale replacing a single measured-value pointer, and has for instance ten divisions equal in distance to nine divisions on the main scale. The interpolated reading is obtained by observing which of the vernier scale graduations is coincident with a graduation on the main scale, which is easier to perceive than visual estimation between two points. Such an arrangement can go to a higher resolution by using a higher scale ratio, known as the vernier constant. A vernier may be used on circular or straight scales where a simple linear mechanism is adequate. Examples are [[caliper]]s and [[Micrometer (device)|micrometer]]s to measure to fine [[Engineering tolerance|tolerances]], on [[sextant]]s for [[navigation]], on [[theodolite]]s in [[surveying]], and generally on [[scientific instrument]]s.
The Vernier principle of interpolation is also used for electronic displacement sensors such as [[Linear encoder#Absolute code|absolute encoders]] to measure linear or rotational movement, as part of an electronic measuring system.