Right as has already been explained,
Draw your line, Sea level 1023 up to another line 6000ft = transition Alt.
Next line for 1013mb 300ft above Sea level, pressure decreases with height, then up another 6000ft = FL60, transition Level, another 1000ft above would be FL70.
Hence FL70 is 1300ish ft above Transition Altitude 6000ft, or as said before 1280ft.
Sorry to get basic but it always worked back in the college!
