I bought a RCBS set 3 years ago. I use em from time to time. especially after my scales dropping or something. I know they are expensive, but for me, they take the guess work out of is my scale right. They increment from .5gr up to like 100gr.

I also found some calibrated bar stock for checking caliber calibrations. I bought some check calibers and picked the ones that were right on, and took the others back.