A while ago, I used to get phone calls from colleagues from all over the university with questions like how to write focussing, with single or double s. As a member of the English department I was expected to know these things. The questions have stopped coming, which may be due to the university-wide use of Microsoft Word which tells you whether you made a spelling error. (I switched this option off, because I often work with 18th-century documents, which consequently get marked with red squiggles all over.)
But I always vaguely assumed that there were different preferences between British and American English, and wonder whether people who rely on Word’s spelling checker are aware of this. But perhaps I’m wrong. I now get increasingly insecure as students correct me for writing things like: “Next time, try focussing on …”. Looking this usage feature up in Fowler (Burchfield’s 3rd edition, 1996), I read that the “proper” spelling is focusing (is it really?), but that “forms with –ss– are used by many printers and publishers”. So what do I do now? Do different publishers’ style sheets include spelling features like this?