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Your first coordinate needs to be in the middle of the grid. Once you have entered the first coordinate it will tell you how many steps away from the chest you are. You then need to go that amount of steps in a diagonal direction. If it gives you the same number of steps as the middle you need to travel that amount vertically or horizontally. If you travel vertically first and it says double your original number then go diagonally that amount of steps. That is where the treasure chest should be, if it isn't there it will be very close.