ABSTRACT
It is certainly possible that the values of Yi are quite accurate, but the corresponding values of Xi are in error. In that case, the deviation would be measured by the horizontal distance illustrated in Figure 4.9. If Xi and Yi both have uncertainties in their values, then the perpendicular distance between a point and the approximating function would be the deviation. The usual approach in approximate fitting of tabular data is to assume that the deviation is the vertical distance between a point and the approximating function, as specified by Eq. (4.143).
