Assertion 2. It is expedient to split diamond grading into two stages.

At the first stage, a basis of a complete or redundant BLResponses system is being built: a computer works with a model, calculating its BLResponses, such as Light Return, Light Leakage, Fish Eye and Contrast. Standardized conditions of lighting and viewing are used for this purpose.

At the second stage, the complete or redundant BLResponses system is used to grade the stone on the basis of formalized experience of experts. The experts' knowledge determines preferences of different groups of customers.

Assertion 3. To complete the above-mentioned tasks, it's necessary to use adequate models of illumination, diamond, and observer. The latter means that psychophysiological properties of human perception should be taken into account. Inadequate modeling of any of these objects may lead to fundamentally erroneous results. To prove this statement, we would like to consider studies performed at GIA. They use methods similar to ours, but obtain essentially different results.