you hear a lot about. this is supposed to be fit tested to actually put it on but one thing to sort of look for is if you have the loops around your head, you are goings to ge a better seal. ventilation. everyone talks about this, chris. i don't think many people really know what it means. i want to show you something here. i just set this up. this is a co2 monitor. >> uh-huh. >> it's sort of a -- a cheap man's version of actually measuring ventilation. how much carbon dioxide, which we all breathe out, is in the air? you want it to be somewhere around a thousand. mine's, what, 1055. i guess, you are making me a little nervous, chris. i'm breathing out more carbon dioxide. but this is -- this is something you can do to try to get a sense of just how much the ventilation is in your area. antigen testing, chris. we talk a lot about the vaccines. but antigen tests. something that you can do on a regular basis. there are several authorized antigen tests now. you can do this daily, if you needed to. and what -- this is if you are feeling fine. but you want to know if you are