Detrending ice data

Hi,

I used "dtrend_msg_n" to detrend a monthly sea ice data(1978-2008). My sea
ice data has ice fraction between 0 and 1. But after detrending it I am
getting values like 1.3. I could not understand how is it going above 1.
I think the function is suppose to remove the trend from the data and give
me the difference between the actual and the trend as +ve and -ve numbers
ranging between -1 to +1 but not above +1.

Thanks,

-- 
"Numbing the pain for a while will make it worse when you finally feel it.
 ~J.K. Rowling"
*****************************************
Soumik Basu
Graduate Student, Research Assistant
International Arctic Research Center
University of Alaska Fairbanks
Fairbanks,Alaska,USA
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