§ Lord Killearnasked Her Majesty's Government:
Why the United Kingdom has adopted the measurements of 79.4mm and 20.5m as standards of eyesight for drivers; and what are the metrical measurements used in other member states of the European Community.
§ Viscount DavidsonThe number plate test was adopted as a practical means of ensuring that an individual's eyesight meets acceptable standards for the purpose of driving. It conforms with the requirements of the First Council Directive for a Common Community Driving Licence (80/1263/ EEC).
Several other member states also employ a number plate test. The precise metric distances at which the number plates have to be read are different because of the variation in size of figures and letters used on the national number plates.