Top: midplane (a) total and (b) thermal pressures of the diffuse gas as functions of . The points and error bars give the mean and standard deviations over t/ t _orb = 2–3. The dotted lines in upper panels show fits P _tot/ k _B = 9.9 × 10 ³ cm ⁻³ K(Σ/10  M _☉ pc ⁻²)(ρ _sd/0.1  M _☉ pc ⁻³) ^1/2 and P _th/ k _B = 2.2 × 10 ³ cm ⁻³ K(Σ/10  M _☉ pc ⁻²)(ρ _sd/0.1  M _☉ pc ⁻³) ^1/2, respectively. Bottom: relative differences between measured midplane pressures and the dynamical equilibrium estimates using Equation (35). The mean midplane pressure P _tot varies only 13% relative to P _{tot, DE}, showing that vertical dynamical equilibrium is an excellent approximation.