?Indeed. Well, that¡¯s, what, 1 part in 1E12?
There are relatively few things one can measure to that kind of precision. In the Radio Science world, they measure the round trip delay of a radio signal to Jupiter and back to a bit better than that.
One can build/buy a device that gets 1E-12 Allan deviation for time over, say, 1000 seconds. See the time-nuts mailing list.
Voltage (and current) are a bit tougher, if only because finding a standard to calibrate against is hard. 24 bit ADCs and DACs are fairly common, and achieve relative accuracies of maybe 2^22. That¡¯s a 1E-7 kind of uncertainty. But finding absolute voltage references is tough - there are semiconductor band-gap references that are maybe 1ppm (1E-6). Doing better as a primary standard would be a Josephson junction which turns voltage into frequency, which can be measured quite accurately, but the need for 4K temperatures makes that challenging. (See Volt-Nuts mailing list - there could be tricks to get better)
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On Jan 26, 2025, at 09:15, ww6x via groups.io <ww6x@...> wrote:
?The impedance of free space is Z? = 376.730313412(59) ¦¸. I, for one, will not stand for any measurement with less accuracy.
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ww6x
On Sun, Jan 26, 2025, at 9:00 AM, Jerry Stuckle wrote:
It is close enough for YOU. It is NOT close enough for everyone.
