Electronic volume-conversion devices (VCDs) or correctors are used to measure standard volumes of natural gas. VCDs are used to convert the measurement flow, temperature, pressure and gas composition under operating conditions into base conditions. The testing and verification of VCDs take into account some specifies and requirements of the standard EN 12405-1 [1] or the recommendation of PTB [2]. National authorities may decide to implement maximum-permissible errors for subsequent or in-service verification. The meter authentication specifies [3] and directive MID [4].Systems for measuring standard gas volumes ( Fig. 1) are comprised of a VCD and a gas meter. Gasvolume conversion devices consist of a calculator and a temperature transducer, or a calculator, a temperature transducer and a pressure transducer that are locally installed. The conversion as a function of temperature, is just called t-conversion, the conversion as a function of the pressure and of the temperature with a constant compression factor, is called pt-conversion, and the conversion as a function of the pressure, the temperature and taking into account the compression factor, is called ptZ-conversion. On the basis of the EN 12405-1 [1] we separate VCDs into type 1 and type 2. Type 1 VCDs are complete instruments, while type 2 VCDs are made of separate elements. Standard volumes of natural gas are measured at the temperature T s = 288.15 K and pressure p s = 1.01325 bar. The VCD calculates and converts the volume of natural gas V, measured by the gas meter at pressure p, and absolute temperature T, into the volume under standard or norm conditions. The VCD's correction factor C is defined on the basis of the standard EN 12405-1 [1] with: Taking in Account Measuring Errors of Volume ConversionDevices in Measuring of the Volume of Natural Gas