Strengths will be in 36, 24, 18, 12, 6, 3, 0. PG and VG. Bottles will be sold with a "JuicePak" of your choice, which will be an adquate amount to flavor your bottle (either 30ml or 15ml) plus 1/3. So if you feel you juice isn't strong enough, you have 1/3 extra you can adjust with.
There...