As members will know, this is not the first quorum call today. The rules on quorum calls have been carefully considered by chair occupants. If the Chair can see them, they are here. In answer to your question, if the Chair is able to see a member, that member is considered to be part of a quorum and the Chair occupant is considered to be one of the quorum.
In the House of Commons on May 7th, 1998. See this statement in context.