Hi Misha, > My own (very unhelpful) diagnosis of the pattern is that, for the > mantissa values: > > 2018.5 should round to 2018 > 2019.5 should round to 2020 The pattern appears to be "round half to even", which you may read about on Wikipedia: http://en.wikipedia.org/wiki/Rounding#Round_half_to_even --Juan