Very low values of this quantity can be measured using the change in resistance of a Pirani gauge filament or using the current generated by gas discharge in Penning gauges. This quantity is decreased by a “roughing” device (10[1])before being decreased further by a booster, such as a Roots blower. Continually operating at low values of this quantity (10[1])can cause oil (10[1])backstreaming. The critical value of this quantity for a van der Waals (“vahls”) gas (10[1])equals the expression “a over 27 b squared.” (10[1])The partial derivative of temperature with respect to this quantity at constant enthalpy is the definition of the Joule–Thomson coefficient. A region where this quantity (-5[1])is (-5[1])very low (10[1])serves (10[1])as thermal insulation for dewars (-5[1])(“DOO-ers”). This quantity (-5[1])decreases (10[1])isothermally in the first step of the Carnot (“car-NO”) cycle. (10[1])For 10 points, (10[1])name this quantity that, (10[1])in a vacuum, (10[1]-5[1])is less (10[2])than (-5[1])“10 (10[1])to the minus 5” (10[1])millibars. (10[4])■END■ (10[4])