However, the "round half up" tie-breaking rule is not symmetric, as the fractions that are exactly 0.5 always get rounded up. This asymmetry introduces a positive 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 higher than the expected value of "y". For this reason, round-to-nearest with the "round half up" rule is also (ambiguously) known as asymmetric rounding.