Hectare

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The hectare (symbol ha, pronounced /ˈhɛktɛər/ or ˈhɛktɑːr) is a unit of area defined as 10,000 square metres, which is primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare ('hecto-' + 'are') was thus 100 ares or 1/100 km2.

When the metric system was rationalised in 1960 with the introduction of the International System of Units (SI), international recognition of the are was withdrawn, though the hectare continued to be recognised as a "unit of measure that may be used with SI".

Contents

History

The metric system of measure was first given a legal basis in 1795 by the French Revolutionary government. The law of 18 Germinal, Year III (7 April 1795) defined five units of measure:[1]

  • The metre for length
  • The are (100 m2) for area [of land]
  • The stère (1 m3) for volume of firewood
  • The litre (1 dm3) for volumes of liquid
  • The gram for mass

Although the law defined the length of the metre, there was no practical way of accurately measuring the metre (and hence the are) until 1799 when the first standard metre was manufactured and adopted.

The standard metre remained in the custody of successive French governments until 1875 when, under the Convention of the Metre, its supervision passed into international control under the auspices of the General Conference on Weights and Measures (GCPM). At the first meeting of the GCPM in 1889 when a new standard metre, manufactured by Johnson Matthey & Co of London[2] was adopted, the are and hectare were automatically redefined.

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