installing moulding - which way is up

we're having camelback crown moulding installed. is there a correct direction for installation?
is the hump or lip supposed to be on the top or bottom or does it not really matter?
thanks
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Go here and click on the small picture. http://www.wishihadthat.com/index.asp ?
PageAction=VIEWCATS&Categoryy4&SetPageSizeu

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Usually it is up. Jack
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