Oxygen Demand Tester Thingy….

Morning all. I have no idea if this would be of interest to anybody, but I have this Normalair Garrett Oxygen Demand System Tester. Not sure of age, but it looks to be all there apart from one of the gauges is missing its glass. Don’t really want to throw it away, but not sure it fit could be of use to anybody!? Sorry Admin if I’m not supposed to advertise on here!!