Normal 6x6 sudoku rules apply. (Place the digits 1-6, once each, into every row, column and 2x3 rectangle). Each digit in a circle must appear in the surrounding 2x2 area. (If a digit appears twice in the circle it must appear twice in the 2x2 area.) The 25 2x2 areas in the grid each contain a 4-digit number (reading from top left to bottom right.) The number in a circle gives the rank of its surrounding 2x2 area, if all these 4-digit numbers are listed from lowest to highest, with rank 1 being the lowest and rank 25 being the highest. All the 4-digit numbers are different, so there are no tied ranks.