_______________________________________Aerodrome elevation (QFE)

                        |           /\          |

                        |         /    \        |

                        |        /     \       | Cold QNH

                        |       /        \        less than QFF

            ______|_ _/_____ \ ___________MSL: QNH = QFF if ISA

                        |

                        | Warm QNH

                          greater than QFF