Sorry for late reply as I was out of office for a service job.
1. Yes Zb is a value should be given for calculation just like % of CO2 and N2 according to the method selected, NX19 or AGA8 GC2 or other. You must have noticed, the Z at measuring condition is not changeable. That is the calculated value.
2. Sorry my knowledge is not better than you on this part. Actually I see different list from your screenshot. I’ll ask factory and reply you.
3. I never noticed the supercompressibility in EK280. I think it’s not in the EK220 system either, right? Maybe Elster EVC doesn’t calculate this value. I’ll confirm and revert.