(gn) is for grains and (g) is for grams. Some digital scales aren’t precise enough to weigh out in grains. If you don’t have a scale dedicated for grains you are doing a disservice to yourself. You can pick up a Hornady or RCBS and even Lyman at a reasonable price.
Edit: when I say some digital scales I’m referring to the ones like my wife used to measure out 6oz. of red meat and so forth...
Also if you are using a digital scale or you sure it is calibrated correctly? The reloading scales will come with brass weights that way you can make sure your scale is calibrated correctly. (think of a standard used for verifying micrometers)