1. The derivation of the following relations may be found in [154] and in: V. V. Novitskiĭ: Delta-function and its Application in Engineering Mechanics (in Russian). Raschet prostranstvennӯkh konstruktsiĭ. Volume 8. Gosstroĭizdat, Moscow, 1962, 207–244.
2. The group method (also the method of means) requires that the sum of errors should be zero in every group, of which there are as many as there are unknown parameters. See Z. Horák: Practical Physics (in Czech), Publishing House SNTL, Prague, 1958, p. 106.