An instrument used to analyze the make-up of various substances, and often used to determine the Btu content of natural gas. CI=Certificate (Independent Producer), CP=Certificate (Pipeline), CS=Certificate (Small Producer), FA=Financial Audits, GP=General Proceeding, GT=General Tariff Change, IN=Investigation, PL=General Policy, RI=Rates (Independent Producer), RM=Rulemaking, RP=Rates (Pipeline), SA=Staff Adjustments (NGPA), ST=Sales under 311(b), transportation under 311(a), assignments under 312 of NGPA, TA=Annual tracking filing, TC=Curtailment Tariff, TF=Tariff Filing, TM=Monthly tracking filing, TQ=Quarterly tracking filing