I have previously given guidance to this effect but it never got incorporated into the main forum rules. I will to to rectify this soon.
In the meantime I'd like to reiterate: whilst some people have a legitimate need/desire for more than one username on this forum (separation of work/personal interests etc), you may not make posts to any given thread using more than one username.
In other words, you can't try and boost your own arguments by signing in with a different name to make a post to agree with yourself!
My partner and I use the same email address at home - makes life easier for us - my partner's log in name is Higher Watha and mine is Mini haha. So we are one email address but two different people with (usually) very differing opinions - hope this is okay with your system as we don't want to change our email address? Please advise. Many thanks.