<P> Though the IPK, the current primary artefact, and its replicas are stored in carefully controlled laboratory conditions, their masses have been subject to fluctuation as a result of poorly understood factors, possibly including handling, cleaning and contamination . The IPK has diverged from its replicas by 50 μg since their manufacture late in the 19th century . This has led to calls to replace the artefact with a standard defined in terms of invariant constants of nature . </P> <P> The avoirdupois (or international) pound, used in both the imperial and US customary systems, is defined as exactly 6999453592370000000 ♠ 0.453 592 37 kg, making one kilogram approximately equal to 7000220460000000000 ♠ 2.2046 avoirdupois pounds . Other traditional units of weight and mass around the world are now also defined in terms of the kilogram, making the IPK the primary standard for virtually all units of mass on Earth . </P> <P> The gram, 1 / 1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice . The final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram (IPK) was derived in 1875, had a mass equal to the mass of 1 dm of water under atmospheric pressure and at the temperature of its maximum density, which is approximately 4 ° C . </P> <P> The kilogram is the only named SI unit with an SI prefix (kilo) as part of its name . It is also the only SI unit that is still directly defined by an artefact rather than a fundamental physical property that can be independently reproduced in different laboratories . Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system are defined in relation to the kilogram, and thus its stability is important . The definitions of only eight other named SI units do not depend on the kilogram: those of temperature (K, ° C), time and frequency (s, Hz, Bq), length (m), and angle (rad, sr). </P>

What unit of mass is 1/1000 of a kilogram