# The Air Quality Regulations 1997, Paragraph 10: Interpretation


An hourly mean is a mean calculated every hour. The hourly mean for a particular substance at a particular location for a particular hour is the mean of the levels recorded, at a frequency of not less than once every 10 seconds, for that substance at that location during that hour.

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Source: https://www.legislation.gov.uk/uksi/1997/3043/schedule/paragraph/10 (the official version)
Page: https://openlegislation.uk/air-quality-regulations-1997/schedule/paragraph-10
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.