The Value score
Value asks the question grading laboratories cannot: is this price good? It positions every listing's price per carat against a daily refreshed statistical baseline for stones of the same kind.
The baseline for a category stores its price quartiles. A listing priced below the first quartile is cheap for what it is; above the third quartile it is expensive for what it is. Half the pillar's weight rides on that percentile position.
The pillar also encodes a real market quirk: magic weights. Demand concentrates at round carat numbers, so a 0.97 carat stone is often materially cheaper than a visually identical 1.00 carat stone. The carat threshold component rewards buying just under a threshold.
Components and weights
| Component | Weight | Label |
|---|---|---|
| price percentile | 50 | Price percentile (50 points): below the first quartile scores 75 to 100, scaling with distance toward Q1 minus 1.5 IQR; between Q1 and the median scores 50 to 75; between the median and Q3 scores 25 to 50; above Q3 decays toward a floor of 5 at Q3 plus 1.5 IQR. |
| price versus median | 25 | Price versus median (25 points): a ratio at or below 0.8 of the category median scores 100, scaling linearly down to 0 as the ratio reaches 1.5. |
| carat threshold | 15 | Carat threshold (15 points): prices step up at the industry's magic weights. A stone just under a threshold (for example 0.97 carat against the 1.00 threshold) earns a bonus of up to 12 points above the neutral 50; a stone just over earns a small penalty of up to 5 points below it. |
| cross-retailer position | 10 | Cross-retailer position (10 points): when the same certificate is listed by two or more retailers, the cheapest listing scores 100 and the most expensive scores 20, scaled linearly. Single listed stones score a neutral 50. |
Price plausibility guard
Vendor feeds that quote tiered rather than per-stone prices can stamp implausibly low prices on large stones. Below a floor of 300 USD per carat, the price is not trusted: the value score is neutralised at 50 so the listing cannot surface as a bargain.