In my own code, I have long used a type similar to boost::interval. In my class, I find these functions useful: T center() const { return (low + up) / 2; } T extent() const { return up - low; } T clamp(T t) const { return t < low ? low : t > up ? up : t; } T wrap(T t) const { return fmodpos(t - low, extent()) + low; } T evaluate(T t) const { return low + t * extent(); } T normalize(T t) const { return (t - low) / extent(); } clamp provides a convenient way to limit a value, changing this ugly thing: double x = max(lower, min(upper, raw_x)); to this: double x = interval(lower, upper).clamp(raw_x); evaluate and normalize map the interval to a normalized interval with values in the range [0,1]. The minor documentation error is at (http://www.boost.org/libs/numeric/interval/doc/interval.htm), where it says, ". . . rounding a+b down and c+d up will suffice." Shouldn't that say "a+c down and b+d up"? Thanks for the good work on this class, Mark Gilbert