When taking a sample of saltwater it is best to use the pipette provided with the unit. Do not dip the end of the refractometer in the water as it can result in saltwater getting in to the callibration screw and causing corrosion. It is also important after callibration to make sure that the screw is dry and the rubber cap is used to protect it, ensuring a long service life.

A small ammount of vaseline or silicone grease can be applied to the top of the screw with a cotton bud to add an extra layer of protection from saltwater ingress.