Arithmetical COMPLEMENT, is what a number or logarithm wants of unity or 1 with some number of cyphers. It is best found by beginning at the left-hand side, and subtracting every figure from 9, except the last, or right-hand figure, which must be subtracted from 10. So, the arithmetical comp. of the log. 9.5329714, by subtracting from 9's, &c, is 0.4670286.
The arithmetical complements are much used in operations by logarithms, to change subtractions into additions, which are more conveniently performed, especially when there are more than one of them in the operation.