I'm not sure what could be used for those specific reference weights, however, you're right about the scale having a harder time reading lower weights. What I commonly do is turn the scale on, apply my weighing surface (typically a notecard),tare, put a 10g weight on to check for accuracy (if accurate I move on to weighing my spice, if not I make any adjustments necessary to get it to read accurately being no more than 2mg off), weigh my spice, then remove the spice, check with a 10g weight again, and then double check the amount of spice again.
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