The "round half down" tie-breaking rule is not symmetric, as the fractions that are exactly 0.5 always get rounded down. This asymmetry introduces a negative bias in the roundoff errors. For example, if the fraction of "y" consists of three random decimal digits, then the expected value of "q" will be 0.0005 lower than the expected value of "y". For this reason, round-to-nearest with the "round half down" rule is also (ambiguously) known as asymmetric rounding.