Measuring Laundry Detergent

The liquid laundry detergent we buy has a series of marks inside the cap to help you measure out the right amount of detergent. Something got lost in translation between marks, the amount of detergent needed and the instructions. There are four levels marked 1, 2, 3 and 4. The instructions say to fill cap between 2 and 3. That's the recommended amount of liquid. Between 2 and 3. Not 2. Not 3. This is a custom cap that is manufactured for this detergent. The amount of the detergent should somehow align with the marks on the cap. Make a new cap. Or will the clothes really not get clean if the instructions said to fill the cap to the 2?