Level-Trol and Multi-Trol

Other than the fact that the 'Level-Trol' seems to be twice the size of the 'Multi-Trol', I have no idea what these are used for. A bit of searching on Google seems to indicate that these are sensors to measure changes in "liquid level, specific gravity or interface level" - most likely of the contents of the tank behind the instruments. Personally, I just thought the lighting was nice.