On Fri, Sep 2, 2016 at 1:31 PM, Bradley White <bww@acm.org> wrote:

Aside: It would be unfortunate, for any expression X, if ((X + 500ms) - (X - 500ms)) was not 1000ms.

I missed a call there, oops.  (f(X + 500ms) - f(X - 500ms)) I can say nothing about.