VEVOR 5CFM Vacuum Pump Stainless Steel Vacuum Pump HVAC 110V AC Vacuum Pump with 2 Gallon Vacuum Chamber (5CFM Vacuum Pump 1 Stage + 2 Gallon Vacuum Chamber)

What measurement is the interior of the chamber? One review said the chamber was a little smaller than advertised. Page states 12 wide x 13.5 high. Also is the pump 1 or 2 stage. Page says both.