Alcoholmeters are for reading alcohol content in distilled spirits only, and will not work on an un-distilled mash.

30cm (12'') long laboratory grade high-accuracy Alcoholmeter. 0% - 100% abv / 0 - 200 Proof reading

An alcoholmeter is used to find the alcohol percentage of alcohol by volume (abv) in a completely dry or distilled liquor.  Because an alcoholmeter does this by through the density of the liquid compared to that of alcohol, any residual sugar or other cause of change to the density will result in a false low reading.  Because there is often a minute amount of unfermented sugar following standard fermentation, along with dissolved carbon dioxide and spent yeast or solids remaining after fermentation, it is very difficult to obtain an accurate reading of the abv in such a liquid.  In addition, an alcoholmeter is increasingly difficult to read at lower alcohol percentages, compounding the problem.  For this reason, it is suggested that you use an alcoholmeter only for the testing of distilled spirits.

The use of an alcoholmeter is very straightforward.  Pour a sample of the spirit to be tested into a tall glass or high chemical tolerant plastic cylinder, leaving enough space for the alcoholmeter to disperse the liquid.  In order to obtain the most accurate reading possible, try to ensure that the liquid is as close to 60'F (15'C) as possible, as this is the temperature that the alcoholmeter has been calibrated to (should your alcoholmeter be calibrated to a different temperature, which should be stated on the meter, ensure that your liquid is at the quoted temperature).  Place your alcoholmeter in the sample and spin it do dislodge any bubbles that may have been in the liquid, and could potentially cause the alcoholmeter to float slightly higher, resulting in a low reading.  Read the mark where the liquid level crosses the stem of the alcoholmeter.  This is your percentage alcohol by volume.

Correction for Brewhaus Premium 0-100% Alcoholmeter:
For every 5 degree above 60^oF subtract 1%abv from reading
For every 5 degrees below 60^oF add 1%abv to reading