Sentence:  In North Greenland distances are measured in <WSD>sinik</WSD>, in 'sleeps', the number of nights that a journey requires. It's not a fixed distance. Depending on the weather and the time of year, the number of <WSD>sinik</WSD> can vary. 
Meaning of the word marked with <WSD> tags:  The amount of distance that one can travel in a day given the current terrain and conditions, a measurement used by the native peoples of Greenland.