This float switch is designed to give the switch level accuracy of a vertical switch, but without the need to mount the switch in the top of the tank.  
This can avoid the need for long, vertically mounted switches, as this switch can be mounted at the required level in the side of the tank.
The switch is configured to give normally open switch action (with no liquid present) when the switch is orientated as shown in the photo above.  
The switch action can be reversed by rotating the shaft through 180°.