Just made another flow calculator which takes as inputs the gas composition. It uses that information to calculate the gas density, ratio of specific heats, and uses the Redlich Kwong equation of state to calculate the compressibility factors. The compressibility factors are not bang on, I could switch to the redlich-kwong-soave equation later, comparing to the AER Directive 17 test cases, it is not always within the +/- 0.25% required, but it is close. You can access the flow calculator here. Expect to see an app coming out which replicates this functionality.