lefthooked, you're making a bigger deal out of it than it really is. Don't worry bout it, so did I at first. I hadn't a clue as to what made sense at first with these calculators. It finally hit me one day.
The top part is referring to your nicotine mix that you have. Let's say you bought it in a PG only base. Forget about the fact that you bought 500ml's of it. That's not part of the equation. You enter in the top that you have 100% PG, and the mg part to the right is the concentrate of nic. Let's say you bought 48mg/ml, you put in 48.
Under that, is the target nic strength. You want it to be 24mg/ml? You put in 24. Under that, is the amount of juice you want to make. You want 10ml's? put in 10. Then comes the flavor. Let's just say you want a total of 10% flavor. If you only use one flavor, you put in 10. If you use two, you put in 5 and 5, or 6 and 4, or 7 and 3. Get the picture? All the different flavors must equal 10, and you put in the percentages for each separately.
Then comes the bottom. All the way to the left it says PG and VG. This is what tripped me up, as I ignored it while trying to figure it out. If you want your mix to be a 70/30 PG mix, then PG you put 70 and VG you put 30. Then you hit calculate. Done. It will give you the figures for everything that goes into the mix.