Length measurement

Length measurement is implemented in practice in many ways. The most commonly used approaches are the transit-time methods and the interferometer methods based upon the speed of light. For objects such as crystals and diffraction gratings, diffraction is used with X-rays and electron beams. Measurement techniques for three-dimensional structures very small in every dimension use specialized instruments such as ion microscopy coupled with intensive computer modeling. Length measurement is implemented in practice in many ways. The most commonly used approaches are the transit-time methods and the interferometer methods based upon the speed of light. For objects such as crystals and diffraction gratings, diffraction is used with X-rays and electron beams. Measurement techniques for three-dimensional structures very small in every dimension use specialized instruments such as ion microscopy coupled with intensive computer modeling. For a discussion of astronomical methods for determining cosmological distances, see the article Cosmic distance ladder. The ruler the simplest kind of length measurement tool: lengths are defined by printed marks or engravings on a stick. The meter was initially defined using a ruler before more accurate methods became available. Gauge blocks are a common method for precise measurement or calibration of measurement tools.