Magtech's application note AN88-10 describes the use of an LG series gauge for the measurement and control of the interface between two immiscible liquids such as water and hydrocarbons.

On some occasions it is necessary or desirable to know the level of both liquids. In some cases the customer has used two gauges on the same tank with one measuring the top fluid and the other monitoring the interface. This is not necessary since two floats and two indicators can be supplied with one gauge.

This technique requires a clever arrangement of the magnet assemblies and has been successfully used in several applications. The indicators are painted red and silver so they are easily distinguished.

For the measurement to be accurate there must be about five inches minimum of the top fluid. When one float rests on top of the other, that is the thinnest layer of the top fluid that can be measured.