You can do it at home Dave! this thing is sold somewhere. I bought mini "scale calibration weight" at my local online store, but i believe there are heavier weight as well. just to see how my scale far off, but not to calibrate it, no option since its china made
i choose 1x300g and 2x100g so i can make combination from 100,200,300,400,500g scale "compensation". i wish they sell 50g as well, but no, and i'm not really a serious punk of this weight calibration that i will search from another side of the world. just cost me few bucks. FWIW if anyone care.