The inclination of each diamond facet should be correctly defined. In other words, a plane should be defined, relative to which the inclination is measured. For instance let us consider a diamond with one symmetry deviation - inclination of table plane on 1 degree.

Registered DiamCalc users can download this model and see it as wire-frame model. Click here to download "TiltedTable.dmc"

To check whether the girdle plane is parallel to the table plane, gemologists got used to examining the stone from the side with a loupe. However, this way allows one to notice possible non-parallelism only if it is strong enough. For instance, an expert equipped only with a loupe would hardly notice a table tilt of 1 degree, as in our example. So, the expert would grade the stone as good, in the sense of the symmetry distortion considered. Should one put the stone into a scanner in the table-down position, scan it, and measure the angles in the model, the stone will appear to be bad, because the scatter of the facet angles amounts now to 2 degrees.

Measuring the cut parameters with a Sarin machine yields a large scatter of facet inclination angles (from 34.2 to 35.6 degrees for the crown facets; from 40.8 to 42.6 degrees for the pavilion ones. Due to this scatter, the existing grading systems would grade such a stone as bad. However, the angles are actually all right, the only problem being the inclined table. Therefore, the stone looks quite good, shows enough brilliance and fire, and is decently graded by the GemAdviser software. Those readers having the registered DiamCalc product are able to work with the draft (wireframe or facet junction) model of this stone and to check the inclination angles for each crown and pavilion facet.

Click here to download "TiltedTable.dmc"

The appearance of this stone strongly differs from that of stones with all pavilion facet angles equal to 40.8 or 42.6 degrees, but is similar to that of a stone with all pavilion facet angles equal to 41.7 degrees. In order to obtain your own opinion you can go to links below and to compare you visual estimations with GemAdviser scores.

Click on any picture below to download corresponding GemAdviser model. Once model is opened by GemAdviser software we also recommend you to click on green "play" button to see this virtual diamond in motion.

Pavilion angle 40.8 Crown angle 34.2	Pavilion angle 42.6 Crown angle 35.6
Launch interactive model	Launch interactive model

Scanned diamond	Pavilion angle 41.7 Crown angle 35
Launch interactive model	Launch interactive model

We can see that a more accurate method for determining and communicating crown and pavilion angles is required. A more correct definition of the pavilion angle is the angle calculated on the base of angle between opposite facets and this reduces the additive error of symmetry distortion with the existing cut grading systems. Therefore our stone has only a very slight symmetry distortion and appears as a stone with a crown angle of 35 degree and pavilion angle of 41.7. However other symmetry distortions exist that this approach will not solve or diminish so it is better to work with a complete 3D model of the stone rather than with a set of its parameters.