The following is the continuation of the unweighted least squares adjustment from Chapter 12 on differential leveling adjustments. The inverse of the normal matrix (Qxx) and the reference standard deviation are derived from this adjustment. This example determines the estimated error in the adjusted elevation differences. Note the symmetry of the level net and the estimated errors in the elevations in the unweighted example and how weights affect this symmetry in the weighted example due to different lengths of lines. This demonstrates the affect weights on an adjustment. In this case, the weights correctly shift uncertainties to thos elevations farther from the control.