In this publication I have attempted to only include the necessary facts, and to explain these carefully. Often other rules are given in books and instructions (for example hydrometer degrees minus 1000 x 2 = grammes of sugar in the must) than are given here. Frequently, a table is shown in which a ruler is used. When this is worked out it does not appear to be correct.

This is because allowance has been made in the figures for the presence of extract or must. Also, the increase in volume with the addition of sugar has been allowed for.

It has been said that one only understands the hydrometer for one day, and nobody can explain it. I have made the attempt. If you now understand the hydrometer, we have achieved the impossible.