Abstract: A calibration system for a measuring device utilizing a photo multiplier tube is provided. The calibration system is intended to provide a stable light source variable over a wide range of intensities which can be used to calibrate the PMT reading using a closed loop feedback circuit. The LED and a photo cell are disposed in a reference block chamber whereby the photo cell is in close proximity disposed perpendicular to the axis of the LED. The LED being dome shaped will direct light energy on to the photo cell, and also peripherally. The PMT is disposed adjacent the LED and at an angle to its longitudinal axis whereby light generated by the PMT simultaneously strikes both the photo cell and the PMT without reflection.

Abstract: A method and procedure for color coding cuvettes used in laboratory tests without contaminating the interior thereof or changing its binding properties is described. In the procedure of this invention, transparent plastic cuvettes are utilized which are flat bottomed and have a depending rim surrounding the flat bottom. The depending surface of the rim then has color applied thereto by a conventional technique either hot stamping, or by ultra-violet cured silk screen printing. In either event, a colored surface is formed on the rim. The transparent walls of the cuvette then by light pipe effect give the appearance that the color surrounds the upper opening of such cuvette when in fact the opening is of transparent plastic.