Re: Mixed measurements
In metric parts of the world, the Feet in aviation aren't a real vertical distance to the ground but an approximate distance based on air pressure which drives the altimeter which is adjusted to a nearby location and adjusted periodically during a flight. Above a point of about 10,000 feet, the altimeter will be adjusted to 29.92 inHg or 1013 mb. This result is in a low or high pressure system, the 500 ft separation of planes is slightly different than 500 ft, but they don't hit each other because they are all using the same reference. A pressure altimeter when calibrated is more accurate than a GPS altitude.
Feet aren't used for horizontal distances in metric countries. Places like Australia which mostly copied the US FAA's rule book down to the section numbers, rounded all the nice round feet to nice round meters (1000 ft became 300 meters, not 305m) but sometimes they rounded up, sometimes down.