An alcoholmeter is an instrument based on the same principle as an hydrometer but the scale shows percentage alcohol and not Specific Gravity.It reads correctly ONLY when used in a mixture of pure water and pure alcohol.If used with the wash resulting from fermentation, it will NOT read correctly as there are other substances in the wash (unfermented sugar, yeast nutrients, etc.) that will cause the density of the wash to be elevated and the percentage alcohol shown on the alcoholmeter will be below the actual percentage alcohol of the wash.