Originally Posted by
Capt Fathom
Webtrak displays altitude referenced to Standard. So you need to know the QNH to see what their actual altitude is.
From the Webtrax Help tab, Other (emphasis mine):
Remember that the aircraft's altitude is displayed. Altitude is relative to mean sea level and not your home location. However if you know the elevation of your home location then you can work out how high above your location the aircraft is at a particular time (the height with reference to your location). You can find more discussion of Altitude in Aviation on Wikipedia.
And Webtrax certainly knows the QNH, it is given as 30.4 [sic] inHg, must be another Oz format I'm not too familiar with.
As a crosscheck, EK407 altitude on rollout is 453 feet, in close agreement with the upwind threshold elevation of 432 feet.