Subtraction is done by adding the ten's complement of the subtrahend to the minuend. The reversal of minuend and subtrahend eases implementation in hardware. We compute the nines' complement of the minuend, 873. The minuend is 704, the subtrahend is 512. However, the 10 is not taken by reducing the minuend, rather one augments the subtrahend. Likewise from "minuere" "to reduce or diminish", one gets "minuend", "thing to be diminished". After the first, the minuend was incremented by one before the second subtraction.