Adjustments to the concentration of water and salts within the urine takes place mainly in the distal parts of the tubules and in the collecting tubules, by altering the permeability of the membranes of cells lining the nephron walls. These changes are brought upon to two hormones, ADH and aldosterone.
Use for Colorimetric and Turbidimetric Determinations. These photometric colorimeters use specific light filters to give readings on a unique KlettTM scale. The readings are directly proportional to the concentration or optical density of a solution, in accordance with Beers Law.
You can either calibrate your display by eye or by using a device called a color calibrator -- or colorimeter -- that you stick on the front of your display. If you have a colorimeter, then I'm going to assume you know how to use it and don't need to read a blog post on the topic.