Flight Level, Transition Layer and when to use it

[172driver]

Just to confuse you a bit more - outside the UK (I think pretty much everywhere), flying semicircular ALT/FL in the cruise is mandatory. No ifs or buts here, except a varying 'XXXX ft AGL' rule, IOW if you are below XXXX ft AGL, then no need to adhere to the semicircular rule. Also, you certainly set your altimeter to 1013 once above the TA. There are even places (Namibia being one), where ALL flying is done on 1013, except in a couple of TMAs. But I digress.....