How to calculate mass flowrate of gas from vacuum pump curve?

Let’s assume we have a liquid ring vacuum pump. The pump curve for this pump is plotted as "suction capacity" in m3/hr vs suction pressure in mbar(a).

How does one calculate mass flowrate of the gas from this curve?
I guess the more specific question is: "Is the plotted volumetric flow of the gas refer to the flow measured at the suction of the pump (at the corresponding pressure) or at the outlet of the pump, where the pressure is atmospheric"?