Please follow the link to our coffee white paper that describes the science behind coffee measurement with a visible spectrophotometer.
The HCCI (Hunter Coffee Color Index) is a linear fit (slope and offset) between the SCAA visual scale and %Reflectance at 640nm. Although the SCAA is a visual scale there are coarse numerical assignments to the visual standards that allow this process.
We provide HCCI, as well as SCAA, because our customers sometime wish to slightly adjust the linear equation to fit instrumentation or standards for which they may have historical data. The SCAA scale is not adjustable by the end user.
Reflectance at 640nm is chosen as it provides significant reflectance differentiation between coffee standards in the visible spectrum. Other similar wavelength bands could be selected but 640nm provides the best discrimination and performance.