More improvements were achieved by Starling in 1972: Z = 1 + ( B 0 − − A 0 R T − − C 0 R T 3 + D 0 R T 4 − − E 0 R T 5 ) ρ ρ + ( b − − a R T − − d R T 2 ) ρ ρ 2 + α α ( a R T + d R T 2 ) ρ ρ 5 + c ρ ρ 2 R T 3 ( 1 + γ γ ρ ρ 2 ) exp ⁡ ⁡ ( − − γ γ ρ ρ 2 )