I almost never use my 5-0-5 scale since I bought the digital. I always check my scales zero with a set of scale weights. I was told by my grandfather (almost 40-years ago) that balance beam scales can get "sticky" and give you an false reading. He always checked his scale with scale weights.
A friend told me Jack O'Connors scale was off by two grains and Jack never knew it. He said some editor wrote this in one of the hunting magazines. I guess someone was using Jack's old reloading setup & checked the scale with scale weights.