Abstract: An apparatus for combining n independent, random binary streams into a single output stream in which the probability of occurrence of a binary "1" is of the form k/2.sup.n. The apparatus which may be easily implemented with a minimum of simple logic elements, includes a combiner for the random streams of the formf = x.sub.n ( . . . x.sub.3 (x.sub.2 x.sub.1 + a.sub.1) + a.sub.2 . . . ) + a.sub.n-1where x.sub.1, x.sub.2 . . . x.sub.n are independent variables representing flat random digital streams and a.sub.1, a.sub.2 . . . a.sub.n-1 are coefficients of the variables x.sub.1, x.sub.2 . . . x.sub.n having the value 0 or 1. Each value of k corresponds to a unique set of coefficients a.sub.1, a.sub.2 . . . a.sub.n-1 so that various probabilities of error may be easily obtained by a series of switches which select the appropriate values of the coefficients.

Abstract: Apparatus for detecting errors in the execution of a sequence of coded inuctions. The apparatus includes a feed-back shift register to generate a digital sequence which is combined with the sequence of instructions to be verified to compute a unique sequence checkword. This computed sequence checkword is compared with a stored, predetermined reference sequence checkword. If any errors have occurred in the execution of the sequence of instructions, the computed and the stored sequence checkwords will disagree, resulting in an output which may be used to halt the process or otherwise cause an alarm. It is an advantage of the apparatus, that it may be easily implemented with a minimum number of logic elements to produce a sequence monitoring device that has an extremely high probability of detecting errors.