Editing Measurement (section)

== Difficulties ==
Since accurate measurement is essential in many fields, and since all measurements are necessarily approximations, a great deal of effort must be taken to make measurements as accurate as possible. For example, consider the [[History of timekeeping devices|problem of measuring the time]] it takes an object to fall a distance of one metre (about 39&nbsp;[[Inch|in]]).  Using physics, it can be shown that, in the gravitational field of the Earth, it should take any object about 0.45 second to fall one metre. However, the following are just some of the sources of [[measurement uncertainty|error]] that arise:
* This computation used for the [[Gravity of Earth|acceleration of gravity]] {{convert|9.8|m/s2}}. But neither of these two figures is exact, but only precise to two significant digits.
* The Earth's gravitational field varies slightly depending on height above sea level and other factors.
* The computation of 0.45 seconds involved extracting a [[square root]], a [[mathematical operation]] that required rounding off to some number of significant digits, in this case two significant digits.

Additionally, other sources of [[experimental error]] include:
* carelessness,
* determining of the exact time at which the object is released and the exact time it hits the ground,
* measurement of the height and the measurement of the time both involve some error,
* [[air resistance]],
* posture of human participants.<ref>{{cite journal|last1=Gill|first1=Simeon|last2=Parker|first2=Christopher J.|title=Scan posture definition and hip girth measurement: the impact on clothing design and body scanning|journal=Ergonomics|date=2017|volume=60|issue=8|pages=1123–1136|doi=10.1080/00140139.2016.1251621|pmid=27764997|s2cid=23758581|url=https://dspace.lboro.ac.uk/2134/33471}}</ref>

Scientific experiments must be carried out with great care to eliminate as much error as possible, and to keep error estimates realistic.