Plan travel to China mainland next month, bought a pre-owned Oregon 550 from from Gumtree, the device come with global basemap (shifting altered or not unknow), 20 meters China Topo, China mainland city NT Pinyin map(according to seller it's venus shifting altered). After installed UK map (downloaded from here) found out it's always shifting out the course. Here comes the question, is it because of the device got map shifting files or caused by basemap? Any solution of it? Many thanks