> Depends on the scope. Calibration is usually performed by an
> internal square wave reference that is usually brought out on
> a terminal on a good quality scope. This is all that's
> necessary for relative frequency calibration. There's usually
> a (cal) position on the horizontal sweep control and a
> screwdriver adjust to get the calbration close. This square
> wave is also useful for adjusting the scope probe
> (capacitance) too. Rick
>

The manual states that the cal output(s) are only to be used for matching
the probes, the frequency is not reliable.

> > Would 50Hz mains AC be accurate enough for LF calibration?
>
> Depends on where you live.  In civilized parts of the world,
> the power line frequency is controlled far more accurately
> than you can see on a scope.
>

I live in the UK. I think we're pretty civilised here :o)

>
> Any crystal oscillator will be far more accurate than any
> error you can see on a scope.
>

Good point. My 20MHz crystals I run my pics on are alledgedly +- 50ppm. That
should probably do the trick.

Thanks for the pointers

Jon

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