a gas meter manufactured prior to the European Measuring Instruments Directive is ±2%. However, the European Measuring Instrument Directive has harmonised gas meter errors across Europe and consequently meters manufactured since the directive came into force must read within ±3%. Meters whose accuracy is disputed by the customer have to be removed for testing by an approved meter examiner. If the meter is found to be reading outside of the prescribed limits, the supplier has to refund the consumer for gas incorrectly measured while that consumer had that meter (but not vice versa). Any refund is limited to the previous six years. If the meter cannot be tested or its reading is unreliable, the consumer and supplier have to negotiate a settlement. If the meter is found to be reading within limits, the consumer has to pay the costs of testing (and pay any outstanding charges). This contrasts with the position on electric meters, where the test is free and a refund is only given if the date that the meter started to read inaccurately can be determined. Remote readouts Remote reading is becoming popular for gas meters. It is often done through an electronic pulse output mounted on the meter. There are different styles available but most common is a contact closure switch. Flow measurement calculations Turbine, rotary, and diaphragm meters can be compensated using a calculation specified in American Gas Association Report No. 7. This standardised calculation compensates the quantity of volume as measured to quantity of volume at a set of base conditions. The AGA 7 calculation itself is a simple ratio and is, in essence, a density correction approach to translating the volume or rate of gas at flowing conditions to a volume or rate at base conditions. Orifice meters are a very commonly used type of meter, and because of their widespread use, the characteristics of gas flow through an orifice meter have been closely studied. American Gas Association Report No. 3 deals with a broad range of issues relating to orifice metering of natural gas, and it specifies an algorithm for calculating natural gas flow rates based on the differential pressure, static pressure, and temperature of a gas with a known composition. These calculations depend in part on the ideal gas law and also require a gas compressibility calculation in order to account for the fact that real gases are not ideal. A very