OK, to sum this up, the NAV database contains information to whether the DME is displaced or not.
It is called
DME bias, and the format is like this (example from
http://x-plane.org/home/robinp/AptNavFAQ.htm#nav.dat ):
34.987022 Latitude of nav-aid in decimal degrees
-106.620384 Longitude of nav-aid in decimal degrees.
5304 Elevation of nav-aid in feet above MSL.
247 Frequency of nav-aid. (Always an integer – so VOR and localiser frequencies multiplied by 100).
50 Range of the nav-aid in nautical miles (first introduced in file version 740)
0.000 Used for several purposes, depending upon the type of nav-aid:
Indicates the slaved variation of a VOR/VORTAC in degrees (ie. how the VOR is aligned compared to true north). This value often differs slightly from the local magnetic variation. Eastern variations are positive, western ones are negative. In the above data, Albuquerque VORTAC has a slaved variation of 13.000 degrees East.
Indicates the heading of a localiser in true (not magnetic) degrees. Also required for glideslopes (when it is combined with the glideslope angle – see below for details) and marker beacons.
Indicates the DME bias in nautical miles – often used for DMEs associated with an ILS that are not located near the runway threshold. This bias must be subtracted from the calculated distance to the DME to give the desired cockpit reading. This is typically used for a DME located in the centre of an airport that serves multiple l ILS approaches, so that the DME will read zero at the threshold of a runway. This is a common set up in Europe.
ILT Identification of nav-aid (broadcast in Morse code in X-Plane). Note that these are not unique.
Isleta NDB Name of nav-aid.