1. A method for analyzing the performance of a testing device for analyzing human bodily fluids which operates over at least two ranges, the method comprising: obtaining a first set of test results relating to human bodily fluids from the testing device over at least two ranges; calculating from the first set of test results an individual range mean for each of the at least two ranges; obtaining a second set of test results relating to human bodily fluids from a group of testing devices that operate over the at least two ranges; calculating from the second set of test results a group range mean and a group range standard deviation for each of the at least two ranges; calculating standard deviation indexes for the testing device from the individual range means, the group range means and the group range standard deviations; forming generally parallel spaced apart data range axes, each relating to a range of operation of the testing device, to facilitate analysis of the performance of the testing device over each range of operation; and plotting all of the standard deviation indexes in relation to the data range axes in such a way that analysis of the performance of the testing device over the at least two operating ranges is provided in a single graphic display.