On Thu, Jan 26, 2012 at 15:15, Intransition <transfire / gmail.com> wrote:

>     |a/b - 1| <= x/b
>
> In your formula it is the same except x is not divided by b. What am I
> missing?
>

a, b, and x are fixed in this case, so let y = x/b, and you have a new
tolerance derived from the old tolerance. That may mean you want to have a
ratio-based comparison have a smaller delta than a difference-based
comparison, but there's nothing much else going on.