I use R regularly for study the validations of different equations, in this case is an equation of cereals which include (barley, wheat, rye, corn, oat, triticale, ..). The monitor function in this case compare the starch values of an instrument consider as the Master (Y axis) and other consider as the Host (X axis).
The idea is to check if there are differences which are important in order to take an action to adjust Bias or Slope and Intercept, or also consider to standardize the instruments.
In this case the Monitor function gives a warning to check if there are groups or extreme samples which can recommends the adjustment of slope and intercept.
And really there is a gap with two groups of samples, so we have to consider in this case what is happening: We have a group of barley samples with lower values of starch and a group with the wheat and corn samples with higher starch values.
In order to evaluate better we have to make subsets and check what is going on with the predictions statistics by groups and proceed the best way.