Firstly who actually questioned the bit about tolerance  Do they understand what Engineering tolerance is about that is why it was WIkilinked  The source itself used the wording for example   Does anybody who has a modicum of understandign of engineering really think that that the tolerance in the UK is going to be less than  of what it is in the US  Maybe it is best to remove that citation altogether  I dont understand your comment about the standard gauge  here is a cut and paste from the source document irrelevant material removed   a  f Track gauge variation from standard  mm gauge I disagree with you about WPPRIMARY  I refer you to my earlier quote on this page No expert advice is needed to understand the relevant part of the  Act