But even if it didn't: Yes, doing some things requires specific training. The same is true for any kind of appraisal system. You won't be able to judge antiques with 15 minutes training, either. Or paintings. Or even something as common as cars.
As for the rating, diamonds are usually rated comparatively, so you had the right approach. If you're a professional diamond grader, you often have a set of reference diamonds. (Yes, that's kind of hard to come by. But diamond grading is hardly the only job that requires specific tools)
The variance should be very low. Part of the certification process from GIA is that you grade a bunch of stones, and you better get it right, or no cert for you. Yes, you can occasionally squabble over a stone that's right on the borderline between two grades.
But even if it didn't: Yes, doing some things requires specific training. The same is true for any kind of appraisal system. You won't be able to judge antiques with 15 minutes training, either. Or paintings. Or even something as common as cars.
As for the rating, diamonds are usually rated comparatively, so you had the right approach. If you're a professional diamond grader, you often have a set of reference diamonds. (Yes, that's kind of hard to come by. But diamond grading is hardly the only job that requires specific tools)
The variance should be very low. Part of the certification process from GIA is that you grade a bunch of stones, and you better get it right, or no cert for you. Yes, you can occasionally squabble over a stone that's right on the borderline between two grades.