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Indexing in reference to motion is moving (or being moved) into a new position or location quickly and easily but also precisely. After a machine part has been indexed, its location is known to within a few hundredths of a millimeter (thousandths of an inch), or often even to within a few thousandths of a millimeter (ten-thousandths of an inch), despite the fact that no elaborate measuring or layout was needed to establish that location. Indexing is a necessary kind of motion in many areas of mechanical engineering and machining. A part that indexes, or can be indexed, is said to be indexable. Usually when the word ''indexing'' is used, it refers specifically to rotation. That is, indexing is most often the quick and easy but precise rotation of a machine part through a certain known number of degrees. For example, ''Machinery's Handbook'', 25th edition, in its section on milling machine indexing,〔.〕 says, "Positioning a workpiece at a precise angle or interval of rotation for a machining operation is called indexing."〔.〕 In addition to that most classic sense of the word, the swapping of one part for another, or other controlled movements, are also sometimes referred to as ''indexing'', even if rotation is not the focus. == Examples from everyday life == There are various examples of indexing that laypersons (non-engineers and non-machinists) can find in everyday life. These motions are not always called by the name ''indexing'', but the idea is essentially similar: * The motion of pins inside a pin tumbler lock, which the correct key can move quickly and easily but also rather precisely into the correct position to allow the lock's cylinder to turn * Indexable driver bits for screwdrivers * The motion of a retractable utility knife blade, which often will have well-defined discrete positions (fully retracted, ¼-exposed, ½-exposed, ¾-exposed, fully exposed) * The indexing of a revolver's cylinder with each shot 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Indexing (motion)」の詳細全文を読む スポンサード リンク
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