> So for grins, I looked at a 4MHz crystal, HC49US4.  Its datasheet says its
> "frequency tolerance: +-50ppm".  Is that 0.005% or about 4 seconds/day?

Yes.  PPM is Parts Per Million.  50ppm = 50/1000000.

(50/1000000) * 3600 sec/hour * 24 hour/day = 4.3 seconds/day


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics