Unit Definition (chain [Ramsden, engineer]) The Ramsden chain is quite different to the Gunter chain. The Ramsden chain was commonly used by American surveyors. It equals approximately 100 feet and is also known as the engineer's chain.
Unit Definition (astronomical unit) An Astronomical Unit is approximately the mean distance between the Earth and the Sun. It is a derived constant and used to indicate distances within the solar system. Its formal definition is the radius of an unperturbed circular orbit a massless body would revolve about the sun in 2*(pi)/k days (i.e., 365.2568983.... days), where k is defined as the Gaussian constant exactly equal to 0.01720209895. Since an AU is based on radius of a circular orbit, one AU is actually slightly less than the average distance between the Earth and the Sun (approximately 150 million km or 93 million miles).
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Length/Distance 
Convert from chain [Ramsden, engineer] to astronomical unit
