1. A method for calibrating a chamber held within an optical scanning instrument so as to enable the instrument to determine volumes of fields of view, or volumes of formed constituents contained in a biological fluid which fluid includes a clear carrier liquid in which the formed constituents in the fluid are suspended, said method comprising: a) the step of providing a container for receiving a quiescent sample of the biological fluid, said container including a sample-receiving sample-viewing chamber which has regions therein of indeterminate varying through plane thicknesses; b) the step of introducing a mixture of a colorant and the biological fluid sample into the chamber and allowing the mixture of colorant and biological fluid sample to spread out in the chamber so as to form a quiescent colored biological fluid sample layer that fills the chamber, said colored biological fluid sample layer including colored regions which include the formed constituents along with colored formed constituent-free portions of the clear carrier liquid; c) the step of providing a calibration area having a known through plane volume or depth, which calibration area is associated with the chamber in a manner which enables a fraction of the colored clear carrier liquid to enter into and fill the calibration area in the container; d) the step of communicating said known through plane volume or depth in said calibration area to the scanning instrument; and e) the step of scanning said calibration area with said instrument in order to quantify a degree of colorant signal intensity emanating from said calibration area so as to enable the instrument to identify and store a colorant signal intensity-to-chamber depth relationship for the container being scanned, thereby enabling the instrument to ascertain depths of subsequent fields of view scanned as a function of color signal intensity emanating from varying depth regions of the sample chamber.