Lee-interesting you mentioned 10% + or -, I just had a pendent appraised & I know the weight of the stones was 25+ct. total. My appraiser basically used the chart & sure enough the weight is @ 9% less than actual weight. In the scheme of things I dont sell but do want to know approximate value & stone correctness to people who ask about the items I show as such & such. It is a useful tool, but should be used carefully-steve...

The original post is very handy information and I used it with classes by the school that is credited for it below the chart. Since I put GTpro on my computer, which I am sure uses the same info as in the charts, I find it easier to just type in a little info and the answer comes up magically.
Robert teaches this information because many of his students become appraisers and will be looking at mounted stones. Best regards, Lee