A plot of 
versus the estimator 
. Random scatter indicates the model is probably
good. A pattern indicates a problem with the model. If the spread in 
increases as 
increases, the errors are called heteroscedastic.
Residual vs. Predictor Plot
See also
EstimatorExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Residual vs. Predictor Plot." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ResidualvsPredictorPlot.html