This application is used for approximation of coffee strenght based on refraction index (nD) and further calculation of extraction yield of the coffee grounds. Refraction index is a number that describes how light propagates through medium (coffee in our case). Refraction index of coffee is measured by refractometers. Using refraction index - TDS dependancy the application computes total dissolved solids (TDS%) of the coffee and shows them in weight percentage.
From coffee grounds and brewed coffee weight is computed Extraction yield (Ext%). This indicates percentage of coffee grounds weight that dissolved to the beverage. During studies on coffee TDS and extraction yield was agreed, that extracting more than 22% of weight from the coffee grounds results in rapid increase of undesirable substances. Extracting less than 18% leads to the underdevelopement of the potential of the coffee and its taste.
When talking about coffee strength the limits are not that strict. Several associations defined their standards for coffee strength (SCAA, SCAE, NCA, GoldCup). Generally they defines what most people feel as right strength.

For measurements of the coffee TDS you need a refractometer. At least its precise and cheap way to determine beverage TDS. True Brew can compute with refractometers displaying results in nD, brix and TDS. Its recommended to use refractometer with accuracy +-0.0001nD, +-0.05 brix, +-0.05 TDS or better. It's not nescessary for the refractometer to have Automatic Temperature Compensation, but thermometer accuracy should be +-0.1 deg C or better.

Measuring coffee samples should be done by someone knowing basics of work in laboratory. All accessory should be clean and dry. First of all stir the brewed coffee and than take a small sample with a pipette. Pour it into cold glass or porcelain container to let it absorb temperature energy and let the sample cool down to the ambient temperature. If measuring espresso, you need to filter the sample through dry and clean paper filter. Than place the sample on the prism of refractometer, that has been previously calibrated with deionized or distilled water. Make sure, that the prism is completely covered by the sample. Wait about 20-30 seconds to stabilize temperatures. Please note, that refractometers thermometer is not used to measure sample on the prism, but to measure ambient temperature. Than commit first reading and displayed result write to the application. To achieve better accuracy you can take second or third reading.