This Level Level Switch can be ordered with level differentials of 1, 2, 3 or 5 inches.  The Also this Float Switch can be ordered with level differentials from 12 to 48 inches.  This large differential provides immunity to nuisance switch tripping due to wave action and turbulence.  

The large differential also provides very low cost single point pump-up/pump-down level control.  No latching relay needed!

Maintenance and checkout is easy using any standard multimeter.   Each unit comes with a detailed instruction manual and parts list.