Find the ratio that you'll need on the side of the cup across the top. In some cases you will have to break down the ratio to the lowest common denominator. Fill the product to a number in the 1st column depending on how much you are mixing. If you need very little product use the #1's. To mix a lot use the biggest numbers. For example, lets say you'll need a medium size amount so you will use the #3's. Fill to the 3 in the first column, then go to the second column and fill to the #3 and if it is a 3-stage ratio go to the third column and fill to the #3.
If your ratio is not on the cup, you can use the scale from 1-10.
These are equal parts or you could use the ounces or mL scales.