Nitous Oxide Cylinder.. pressure gaudge..

The picture is self explanatory One Nitrous Oxide cylinder when connected to anaesthesia machine showed the pressure to be 100kPa, where as the other cilder fitted to the other port showed 50kPa. When the cylinders were interchanged the pressure  in the gauge also changed.
So it was presumed this cylinder is mixed with some other gas which is exerting this additional pressure.
As there was noscope to examine this gas. , the gases from the cylinder was discharged to open atmosphere slowly  in an open space.
So all are cautioned that  a very high pressure in N2O cylinder should be looked at. There were some discussion that there is no need for Pressure gaudge in N20 side as the pressure is always  the same as long as  the last  drop of liquid N2O is present. But here is a scenario where the pressure gaudge  could help us to avoid a possible critical incident in Anaesthesia.