1. A method for procuring platelet rich plasma (PRP) from a sample of whole blood in a vial, the method comprising the steps of: separating the whole blood into layers through centrifugation with an upper layer containing platelet poor plasma (PPP) and a PRP layer disposed below the upper layer and containing PRP; adjusting an end point of a first range of motion of an extractor relative to a position of the PRP layer by setting the position of a stop against which an abutment associated with the extractor engages at the end point, the position of the stop being determined by aligning with the PRP layer an indicator associated with the stop; moving the extractor through the first range of motion through the vial, PPP passing out from the upper layer through the extractor; and after the extractor reaches the end point of the first range of motion, extracting the PRP through the extractor and collecting the PRP.