In UV-Vis spectroscopy, we usually assume Beer's law to be valid: the
absorbance of a compound is proportional to its concentration. With
higher concentrations, this may no longer be true. The absorbances then
are lower than expected. Suppose someone ignores this effect and calculates
the best line from a set of calibration samples.
What would you expect the plot of the residuals
(true values minus fitted values) to be like when the
highest concentrations cause Beer's law to fail?