Determining a beginning and an end creates a dilemma for measuring LUT plots. There are many variables playing on where to start the plot-line and where to end it. The total distance from one end of the CRD of a hexamer to the other CRD can be measured in at least these ways. 1. brightest spot to brightest spot, 2. straightest line (whether that means beginning or ending the line in a place where one of the three elements of the CRD are spread apart creating a darker and shorter line path.