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short communications
An error has occurred in the Abstract of the paper with the above title (Wilson, 1967). In the last line but one `fixed-count timing' should read `fixed-time counting'. A superscript 2 has been omitted from equation (93), p. 895. This equation should read σ2ft(Am) = Σj[cos(2πmj/R) − Am]2Ij.