I assume we're talking short distances since you are in the bowhunting threads .. this is what I do when I don't have my Nikon ( might not be what you're askin but .. here ya go.. get REAL GOOD at 10 yds .. practice , different places , different environments , then you do 10 yd increments .. might sound hard but I know I can do it so anybody can do it .. with practice you can get w/ in 2 yds pretty consistently say out to 40 yds .. beyond that you can visually cut a distance in half and mentally measure half and double it . I shot a buck the other day and guessed 80 yds and it was actually 88 .. I know that's nfg for bow but 80 is very extreme for my bowhunting anyway ..hope you'll at least try it .. old 3d trick