So, it looks like so far we have: next(val) prior(val) and either of representation_distance(a, b); discrete_distance(a, b); Whilst I'm normally all in favour of "long_meaningful_names_with_underscores", next() and prior() do look OK to me: especially so long as they're in namespace boost::math. Like Paul, I'm still looking for the right "killer name" for the *_distance function, I quite like "maddock_metric" but I doubt anyone will know what that means :-) Given that this function is inherently related to the "units in the last place" metric, I wonder if we can compose a name from that? Maybe extending the API slightly how about: T upl_distance(T, T); // "representation distance" T relative_distance(T, T); // AKA relative error. T ulp(T); // distance between arg and next(arg) Thoughts? Thanks, John.