If you want to know exactly how alcoholic your champagne is before you drink it, you can take gravitational readings and follow a simple formula.
Once you've dissolved the sugar in all ten litres of water you need to take your first reading.
Fill the hydrometer tube up to about 2 inches from the top with the sugar water.
Insert the hydrometer giving it a little spin as you do so. The hydrometer will slowly sink until it stops and bobs up and down gently.
When the hydrometer comes to a stop, look at where the liquid intersects the markings on the hydrometer.
Record the gravity reading - this is called your 'Original Gravity'.
Repeat this process immediately before bottling. This is called your 'Final Gravity'.
To get your ABV, subtract the Original Gravity from the Final Gravity then multiply this number by 131.25.
If you like formulas then use the following:
(FG - OG) x 131.25 = ABV %