The optimum knots ordinate formula in the least square sense is derived by computing coefficient matrix and curve vertexes under the specified subsection knots abscissas conditions.

Making use of the points measured on the drum helical curve of concrete-mixer truck, the helical Angle formula of the helical curve is obtained by means of least square method.

There are two kinds of algorithmic structures for the method of weighted recursive least squares (WRLS) corresponding to the matrix reversing (MR) formula or the QR decomposing theorem.