It's complicated. However, in FSX if you are using the latest ADE from Scruffy Duck, you can (if you want) open the airport file, look and see if ILS/DME is checked. If it's not, you can check it and set the range for the DME. You'll need to compile your changes and save it in the addon scenery for that particular airport. This will give you the ability to see distances on your DME equipment. May not be right (maybe the airport doesn't have dme) but it certainly works if you want to measure distances to the runway.