I LUV my unit but (isn't there always a but) I have difficulty opening and closing. I feel like I am missing some basic trick. I can't believe that all the med patients twist that top on and off with no trouble. When I was a kid my Dad would toss me the car keys and send me to fetch from trunk of car. Looking at all the keys on ring I would ask which one? Dad would yell back square key, round key and I would hold keys to light and look at the tips and they would all look similar. When I turned 30 a friend told me to move my thumb and low and behold all the keys had different shapes at the top. What I am trying to say is "You don't know what you don't know until you know it." If you think of an easy way in and out of top of NO2 please help an old dog out. If that is just the way it is I guess I will have to toughen up and do hand exercises.