Anthony Fremont wrote:

If someone doesn't need traceable calibration, then why should they pay
for
it? Especially if they have the resources to do it themselves. I'm
thinking of buying a cheap used Rb time base from e-bay so I can cal my
old Protek freq counter and adjust the timebase on my Hitachi scope, it's
certainly cheaper than having it done. Using a PIC driven by an ordinary
can xtal, and a quartz wris****ch of known accuracy, I was able to tweak
the
xtal to within about 1-2ppm over the course of a week or two. Of course
you know that's impossible, don't you?

I don't think the oscillator on a PIC would be good to 2ppm absolute
accuracy even with a very good xtal, unless you FIRST calibrate it against
something that has already been calibrated, therefore it doesn't get you
far. It will however be good enough to calibrate your scope since that
would only need 1% or so, and any old crystal should achieve that, even
with a fairly primitive oscillator. For frequency calibration, your best
bet is to receive an off-air standard, for example GPS or in many countries
there are low frequency standard transmissions (50kHz, 60kHz, 77.5kHz or
others, look up which ones are available in your country). It is quite
feasible to build your own receiver for these. These transmitters are
maintained to a higher accuracy than any piece of hardware that a hobbyist
could afford (e.g. 2 parts in 10^12).
http://www.npl.co.uk/time/msf/ctm001v05.pdf

Chris