The water hardness setting is determined by the hardness of your water supply. If you do not know the hardness of your water supply you can take a sample into Sears and they can test the sample and give the hardness level. Once you know the hardness level of your water supply you set the hardness level.
The higher the setting means harder the water supply. If your water supply hardness is 15 gpm (grains per gallon) then you set the hardness level to 15.
Since you did not submit the model number, I added some general information taken from a typical userâ€™s manual on "Setting Water Hardness Number" in the image below.