Editing Vernier scale (section)

===Zero error===
Zero error is defined as the condition where a measuring instrument registers a nonzero value at the zero position. In case of vernier calipers it occurs when a zero on main scale does not coincide with a zero on vernier scale. The zero error may be of two types: when the scale is towards numbers greater than zero, it is positive; otherwise it is negative. The method to use a vernier scale or caliper with zero error is to use the formula
: ''actual reading = main scale + vernier scale − (zero error).''

Zero error may arise due to knocks or other damage which causes the 0.00&nbsp;mm marks to be misaligned when the jaws are perfectly closed or just touching each other.

[[File:5783metric-micrometer.jpg|thumb|Vernier micrometer reading 5.783{{nbsp}}±{{nbsp}}0.001&nbsp;mm, comprising 5.5{{nbsp}}mm on main screw lead scale, 0.28{{nbsp}}mm on screw rotation scale, and 0.003{{nbsp}}mm added from vernier.]]
[[File:Vernier scale zero error +0.10.gif|thumb|When the jaws are closed and if the reading is 0.10{{nbsp}}mm, the zero error is referred to as +0.10{{nbsp}}mm. The method to use a vernier scale or caliper with zero error is to use the formula 'actual reading = main scale + vernier scale − (zero error)' thus the actual reading is 19.00 + 0.54 − (0.10) = 19.44]]

''Positive zero error refers to the case when the jaws of the vernier caliper are just closed and the reading is a positive reading away from the actual reading of 0.00{{nbsp}}mm. If the reading is 0.10{{nbsp}}mm, the zero error is referred to as +0.10&nbsp;mm.''

Negative zero error refers to the case when the jaws of the vernier caliper are just closed and the reading is a negative reading away from the actual reading of 0.00{{nbsp}}mm. If the reading is 0.08{{nbsp}}mm, the zero error is referred to as −0.08{{nbsp}}mm.

If positive, the error is subtracted from the mean reading the instrument reads. Thus if the instrument reads 4.39&nbsp;cm and the error is +0.05, the actual length will be 4.39 − 0.05 = 4.34.
If negative, the error is added to the mean reading the instrument reads. Thus if the instrument reads 4.39&nbsp;cm and as above the error is −0.05&nbsp;cm, the actual length will be 4.39 + 0.05 = 4.44.
(Considering that, the quantity is called zero correction which should always be added algebraically to the observed reading to the correct value.)

: ''Zero error (ZE) = ±n × least count (LC)''