As of 2009, the European Union had issued two units of measurement directives. In 1971, it issued Directive 71/354/EEC, which required EU member states to standardise on the International System of Units (SI) rather than use a variety of CGS and MKS units then in use. The second, which replaced the first, was Directive 80/181/EEC, published in 1979 and later amended several times (in 1984, 1989, 2000 and 2009), which issued a number of derogations to the United Kingdom and Ireland based on the former directive.
Directive 71/354/EEC
When the first units of measurement directive was issued, the six members of the EEC had been using the metric system for a hundred years or more. During that time the metric system had undergone a number of changes, particularly in science and engineering. Some industries were based on the CGS variant of the metric system and other on the MKS variant. In 1960, the CGPM published the International System of Units (SI), a coherent version of the metric system based on the MKS variant. Directive 71/354/EEC sought to rationalise the system of units within the EEC by standardising on SI.
The directive catalogued the units of measure that were permitted for measuring instruments (for instance scales), measurements and indications of quantity expressed in units for economic, public health, public safety and administrative purposes. The catalogue was consistent with the SI standard. The directive explicitly proscribed a number of mainly CGS units of measure that were not to be used after 31 December 1977.
The directive explicitly exempted member states from having to use those units of measure in the catalogue in situations where other units of measure had been laid down by international intergovernmental conventions or agreements in the field of air and sea transport and rail traffic.
Denmark, Ireland and the United Kingdom joined the EEC in 1973. The directive had little impact in Denmark which was in a similar situation to the other EEC member vis-à-vis the use of metric units. Ireland and the United Kingdom were in the process of metrication programmes and the directive was consistent with those countries policies as they stood at the time. The three new member states had five years to implement this directive (as well as all other directives that had been published by the EEC).
Directive 80/181/EEC
By the late 1970s, the metrication programme in the United Kingdom had lost momentum. In particular, the government had decided to postpone the metrication of road signs. Furthermore, the metrication of trade in many consumer areas had not been completed. The United Kingdom asked the EEC for a derogation to permit the continued use of imperial units. The result was a repeal of Directive 71/354/EEC and its replacement by Directive 80/181/EEC. The principal changes were:
A number of units that had been proscribed under Directive 71/354/EEC could continue to be used until the end of 1985. A number of imperial units including the pound, ounce, yard, foot, inch, gallon and pint could continue to be used until the end of 1989. The mile, yard, foot and inch could be used on road traffic signs, distance and speed measurement, pints could be used for the sale of milk in returnable containers and for the measurement of draught beer and cider, acres could be used for purposes of land registration and troy ounces could be used when dealing with precious metals until a date to be determined by the states in question. Supplementary units were permitted until the end of 1989.