The Alcometer is used to measure the alcohol content by floating it in the spirit; as the alcohol's viscosity is lower than that of water, its alcohol content increases as the hydrometer floats further down. The reading is taken at the point where the surface of the spirit intersects the scale. A temperature conversion of 20°C = 68°F is applied for accurate results, and the hydrometer should only be used before any additives are added.
An Alcometer (as opposed to a Wash, Wine & Beer Hydrometer) is used to test the strength of your spirit. Additives such as flavouring and Liquid Glucose will distort the hydrometer readings. Alcometers should only be used to test spirit before any additives such as flavouring or liquid glucose are mixed.