This is discussing a formula for calculating the Quantity In or quantity of material or signal received by one station from another station. It states that a sample will be taken and that this sample will be deducted from the output of the preceding station and that this sample material or signal will be designated, for the purposes of the calculation, as being reject signal or material. I consider that a revision of the 'to' to a 'from' will clarify the intentions of the sentence slightly.
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