This question was answered here recently - 9 months in an 18 months period. But not sure I'm understanding. (where's the 'duh' emoticon?) Sorry, I'm right-brained.
Does that mean one can stay for six months of each year? 12 months of each 24 months? 18 months of each 36 months? I've googled it with no luck - other than finding the 9/18 time period and also done a search here.
Friends are asking how long they can come to visit once I'm living back in NZ. Maybe I should just tell them there's a one week limit each 12 month period!