>
>>  ...In civilized parts of the world, the power line frequency is
>controlled far more accurately than you can see on a scope...
>
>Sorry, that's me who got restricted to be not free to comment
>this kind of statements (perhaps due to I live in "wrong" i.e.
>"uncivilized" from someone's point of view part of the world).

The powerline frequency is only correct in the long term. (hours)

I remember watching our school clocks visibly slow, when the local steel mill fired up.

A canned crystal oscillator will give you a nice accurate timebase.
You can build one, but you'll need to get the xtal loading caps right before you'll get the right frequency..
You can compare a 10 MHz oscillator to the WWV carrier, using a shortwave receiver.
WWV broadcasts on 2.5, 5, 10, 15, and 20 MHz, but the 10 MHz is the most consistently easy to pick up, at least around here.  Take that 10 MHz canned oscillator, and divide it down by several stages of /10's, with socketed, buffered outputs, put it in a cabinet, and you have an nice reference generator.

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