Basic facts:

1 litre of water weighs 1 kg (1.000 grammes)

1 litre of alcohol weighs 0,8 kg (800 grammes)

1 litre dissolved sugar weighs 1,59 kg

When the must begins to ferment it has a high sugar content.

The hydrometer reading is 1080 degrees, and as the sugar ferments out the hydrometer sinks lower and lower.

Take readings of the must.

If the lock is "plopping" it is fermenting.

If the lock is silent, take a reading again after at least 24 hours.

If the hydrometer reading is lower, the wine is fermenting.

If the reading has not fallen, check the wine to see if it ready. Refer to the relevant table.

If fermentation has not started (takes 24-48 hours), contact your nearest home brew shop.