How do scientist measure salitinity of ocean water?

You can find the measure of salinity with a cup and a sticker at the bottom of it. You will put what you are measuring in the cup and see if the sticker is clear, about clear, foggy, or blacked out. then if it is clear it is 0 jtu's if it is about clear it is 40 jtu's if it is foggy it is 80 jtu's and if it is blacked out it is 400 jtu's.