Does Hach have a general statement that explains how the solids calibration correlates to measured value?
TSS portable solids measurement explanation
Yes, a single point calibration draws a straight line from the probes zero point to the point of calibration; however the mathematical transformation of the different signals of the different detectors is nonlinear. When a calibration curve consists of 3 points the curve is created by connecting the straight lines. The course may not hit the zero e.g. because the medium itself is colored and absorbs light.