I know abbot recommend the outside of the arm , and I know if your new to the system its the obvious place to put it but in my experience ( of several years ) of using the Libre , there are other places to put it , definetly on the inside of the upper arm works for me , I’ve checked the Libre against a finger prick and readings are definetly acceptable .and I’ve not had any bumped off, I’m a bit of an experimenter and have used different places for my sensor , chest belly to name but 2 , as a side note , if I have had to get a new from Abbot due to a fault , I’ve never been asked where I put my sensor , I imagine if I was I would say outside of arm , oh what a little devil I am hehehe