error$$=\sum_{i=1}^{n}\left(x_{i}-\bar{X}\right)=0$$
$\begin{array}{c} {\sum_{i=1}^{n} x_{i}-\sum_{i=1}^{n} \bar{X}=0} \\ {\sum_{i=1}^{n} x_{i}=\sum_{i=1}^{n} \bar{X}} \\ {\sum_{i=1}^{n} x_{i}=n \bar{X}} \\ {\sum_{i=1}^{n} x_{i}=\sum_{i=1}^{n} x_{i}} \end{array} \nonumber$