I think it adjusts with weighing the garments at the start of the wash too. So say if you only have a couple of items in the drum to wash it will use less detergent than if you had a full drum of washing , so that it does not overdose/underdose the detergent and fabric conditioner. - even dearer models could have an extra sensor in them called a turbidity sensor that throughout the wash monitors the detergent in the drum and can add even more detergent if the water is dirty/heavily soiled garments... so I really dont know why they let you select low/med/high if the machine detects by weighing at the beginning what amount/dose of detergent is needed for that particular wash cycle
