Editing Speedometer (section)

===International agreements===
In many countries the legislated error in speedometer readings is ultimately governed by the [[United Nations Economic Commission for Europe]] (UNECE) Regulation 39,<ref>{{cite web|url= http://www.unece.org/trans/main/wp29/wp29regs21-40.html |title=UNECE Transport Division – Vehicle Regulations – Addenda to 1958 agreement – Regulations 21–40 |publisher=UN Economic Commission for Europe |access-date=30 January 2015}}</ref> which covers those aspects of vehicle type approval that relate to speedometers. The main purpose of the UNECE regulations is to facilitate trade in motor vehicles by agreeing on uniform type approval standards rather than requiring a vehicle model to undergo different approval processes in each country where it is sold.

[[European Union]] member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers<ref>{{cite web|url= http://eur-lex.europa.eu/eli/reg/2004/39(2)/oj |title=Regulation No 39 of the Economic Commission for Europe of the United Nations (UN/ECE) — Uniform provisions concerning the approval of vehicles with regard to the speedometer equipment including its installation |work=European Commission |access-date=8 April 2017}}</ref><ref>{{cite web |url= http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31997L0039:EN:NOT | title = Commission Directive 97/39/EC of 24 June 1997 adapting to technical progress Council Directive 75/443/EEC of 26 June 1975 relating to the reverse and speedometer equipment of motor vehicles |work=European Commission | date = 24 June 1997 |access-date=7 January 2007}}</ref><ref>{{cite web |url= http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32000L0007:EN:NOT | title=Directive 2000/7/EC – speedometers for two- or three-wheel motor vehicles |work=European Commission | date=20 March 2000 |access-date=7 January 2007}}</ref> are similar to the UNECE regulation in that they specify that:

* The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
* The indicated speed must not be more than 110 percent of the true speed plus {{cvt|4|km/h}} at specified test speeds. For example, at {{cvt|80|km/h}}, the indicated speed must be no more than {{cvt|92|km/h}}.

The standards specify both the limits on accuracy and many of the details of how it should be measured during the approvals process. For example, the test measurements should be made (for most vehicles) at {{cvt|40|,|80|and|120|km/h}}, and at a particular ambient temperature and road surface. There are slight differences between the different standards, for example in the minimum accuracy of the equipment measuring the true speed of the vehicle.

The UNECE regulation relaxes the requirements for vehicles mass-produced following type approval. At Conformity of Production Audits the upper limit on indicated speed is increased to 110 percent plus {{cvt|6|km/h}} for cars, buses, trucks, and similar vehicles, and 110 percent plus {{cvt|8|km/h}} for two- or three-wheeled vehicles that have a maximum speed above {{cvt|50|km/h}} (or a cylinder capacity, if powered by a [[heat engine]], of more than {{cvt|50|cm3}}). European Union Directive 2000/7/EC, which relates to two- and three-wheeled vehicles, provides similar slightly relaxed limits in production.