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A pound lock has a chamber with gates at both ends that control the level of water in the pound. In contrast, an earlier design with a single gate was known as a flash lock. [4] Pound locks were first used in China during the Song dynasty (960–1279 CE), having been pioneered by the Song politician and naval engineer Qiao Weiyue in 984. [5]
A short pound on the Chesterfield Canal in England, United Kingdom. A canal pound (from impound), [1] reach, or level (American usage), is the stretch of level water impounded between two canal locks. Canal pounds can vary in length from the non-existent, where two or more immediately adjacent locks form a lock staircase, to many kilometres/miles.
Metrology is a wide reaching field, but can be summarized through three basic activities: the definition of internationally accepted units of measurement, the realisation of these units of measurement in practice, and the application of chains of traceability (linking measurements to reference standards).
In metrology (the science of measurement), a standard (or etalon) is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity. [1] Standards are the fundamental reference for a system of weights and measures , against which all other measuring devices are compared.
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The principle of coherence was successfully used to define a number of units of measure based on the CGS, including the erg for energy, the dyne for force, the barye for pressure, the poise for dynamic viscosity and the stokes for kinematic viscosity. [29]
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Weir at the main (Western) head of the Swift Ditch Remains of the old pound lock near the Eastern head of the Swift Ditch. The Swift Ditch is a 2 km (1.2 mi) long artificial channel that formed a short-cut for river traffic to and from Oxford, across a meander of the River Thames in England.