Jawaban Terbaik:  Normalising any measurement requires that the STP (standard temperature and pressure) values be defined 1st as they are often different for different countries ie 

USA 

Tref = 20 or 25 degC (depending on the measurement standards) Pref = 29.92 inHg 

Europe, Australia, NZ, UK 

Tref = 273.15 degK = 0 degC Pref = 1013 hPa 

Converting raw m3/hr to Nm3/hr is a simple application of Charles Law multiplying ratios of true and ref Temp and Pressure values as follows.. we can ignore the hr term as it is applied throughout 

if m3=1 and Pactual=1025hPa and Tactual=21degC 

Nm3 = m3 x Pactual/Pref x (273.15+Tref)/(273.15+Tactual) 

Nm3 = m3 x Pactual/1013 x (273.15+0)/(273.15+21) 

Nm3 = 1 x 1025/1013 x 273.15/294.15 

Nm3 = 1 x 1.01185 x 0.92861 

Nm3 = 0.939 m3