The BM 26 operates on the principle of communicating vessels. The measuring chamber is connected adjacent to the tank so that the same conditions are obtained in the chamber as those in the tank.

The float is equipped with a system of permanent magnets to transmit measured values to the local indicator.

The magnet system of the float activates either the magnetic flaps according to the liquid level, or a movable follower magnet in the indicating section of the indicator depending on the method of indication chosen.

The column of reversed yellow magnetic flaps, or the vertical position of the follower magnet, indicates the liquid level.