Sounds like to me that education as to Xara's approach is the key. Perhaps this could be reinforced somehow in the Help file or something as basic as a notation in the Options > Units dialog or tooltip for the input box or an alert when changing units (which could be turned off by the user once they "see the light")


A really BIG plus for me with a document storing settings (like Print Options > Output settings) has been when passing a file onto less experienced users ... I can make life easier for them as I know somethings won't automatically be overridden when they open the file.