Abstract: Apparatus for measuring the level of an item in a liquid including first and second light transmitting cylinders, a first piston and an associated conduit for conducting liquid to the first cylinder, a second piston and an associated conduit for conducting liquid to the second cylinder, a third piston and an associated conduit for conducting indicator solution to the second cylinder, a light source for transmitting light through the first and second cylinders, and a detector for measuring the difference in light transmissibility of the liquids in the first and second cylinders and providing an output depending thereon. A method of testing the level of an item in a liquid including the steps of providing a first sample of the liquid containing the item, providing a second sample of the liquid with a measured amount of indicator solution therein, comparing the light transmissibility of the first and second samples, and providing an output which is a measurement of the level of the item in the liquid.