Used the 1870 since its inception, now trying out 1871. The 1870 separated out the school of kokanee to show individual fish lenghts, 7-13” mostly, and the same school on the 1871 lumped them together 25-45” for same fish. The numbers r also small and hard to read on the 1871 with no size adjustment like the 1870. The best thing i like about the 1871 is the A scope on both windows in bottom lock however.