>
>I have bread boarded an astable 555 timer circuit using my scope to
>measure the period, but with known cap values this is not particularly
>accurate...

It should be pretty accurate, as long as the resistor values are known.
Most caps are pretty sloppy though, -10 / +50% isn't uncommon in electrolytics.

You can measure their impedance at 1kHz, and work from that, but what the 555 does, effectively, is measure the R/C time constant. Since R is known, C is the variable. At room temperature, with a steady voltage, the results should be more accurate than the cap.

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