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It is assumed that a crystal structure P1 is fixed and that the 31 non-negative numbers R1, R2, . . ., R6; R12, R13, . . ., R56; R123, R124, . . ., R156 are also specified. The random variables (vectors) h, k, 1, m, n, p are assumed to be uniformly and independently distributed in the regions of reciprocal space defined by and |Eh| = R1, |Ek| = R2, . . . , |Ep| = R6; (1) |Eh + k| = R12, |Eh + l| = R13, . . . , |En + p| = R56; (2) |Eh + k + l| = R123, |Eh + k + m| = R124, . . . , |Eh + n + p| = R156; (3) and h + k + l + m + n + p = 0. (4) Then the structure invariant φ = φh + φk + φl + φm + φn + φp, as a function of the primitive random variables h, k, l, m, n, p, is itself a random variable, and its conditional probability distribution, given (1), (2) and (3), is derived from the main result of the previous paper [equation (3.1); Fortier & Hauptman (1977). Acta Cryst. A33, 694-696.] and compared with the distribution when only (1) is given. The distribution leads to estimates for cos φ in terms of the 31 magnitudes (1), (2) and (3).