Draw contours below - if checked, a contour plot will be drawn in the bottom plane of the cube. The contour levels will correspond to those selected on the Contours tab. Number of divisions - determines how many lines will be drawn on the surface plot. From, to, by - defines the contours to be plotted. Resolution - defines the resolution of the grid at which the function is evaluated.
Higher resolutions give more accurate results but are more computationally expensive.
In moderately sized data sets, Studentized residuals of 3.0 or greater in absolute value may well indicate outliers which should be treated separately. Points with more than 3 times the average leverage are included on the list. Mahalanobis distance - measures how far away from the centroid of the data each row lies in a multidimensional space defined by the independent variables. You should carefully examine any rows on this list to insure that they represent valid data, since they are especially influential in determining the fitted model. Any increase in scatter around the line as the predicted values increase could indicate the presence of heteroscedasticity, i.e., non-constant variability of the residuals.