Calorific Values and Properties of Natural Gas per ISO 6976:2016 // Calculates calorific values (gross and net), density, relative density, and Wobbe indices together with their standard uncertainties from natural gas composition, implementing the method of ISO 6976:2016 "Natural Gas Calculation of calorific values, density, relative density and Wobbe indices from composition". Uncertainty propagation follows Annex B of that standard. Reference: International Organization for Standardization (2016) https://www.iso.org/standard/55842.html.