The prime unit of measure for aviation (altitude, or flight level) is usually estimated based on air pressure values, and in many countries, it is still described in nominal feet, although many others employ nominal metres.
航空的主要计量单位（高度或飞航空层）通常基于气压值推算，在许多国家依然以英尺表示，尽管许多其他国家使用米。