The bad news is that there are 5 or 6 different standards (temps and pressures) used for measuring natural gas, but the good news is that the meters readings are easy to standardize.

The equation is from the ideal gas law, which can be shrunk down to P1*V1/T1 = P2*V2/T2. What this is saying is that the amount (mass) of gas isn't changed, but the pressure, volume and temp are.

For your case, [ (3 + 1 bar) * (1 m3) / (outside temp + 273) ] = [ (.6 + 1 bar) * (unknown) / (inside temp + 273) ]. The +1 is for absolute pressure since the gauges read relative pressure, and the +273 is to get from Celsius (relative) to Kelvin (absolute).

In a better form { [ (1.6 bar) * (meter reading at furnace) * (outside temp + 273) ] / [ (4 bar) * (inside temp + 273) ] } = volume from furnace on the outside meter.

The symbol for standard cubic meter is Sm ³. Standard Cubic meters indicate how many cubic meters there is of a substance when the substance has a temperature of 15 ° C and the pressure equal to 1.01325 bar (standard atmospheric pressure).

Regards Woody