On Tue, 11 Dec 2007 00:36:02 GMT, Owen Duffy wrote:

I mean't literally a point sample, and I doubt that we can manufacture a
probe for either voltage or current that has zero dimensions (ie is
influenced ONLY by conditions at a point of no physical size.).

Hi Owen,

I would say that is arguable given my exposure to research in
Nanotechnology. I've seen one molecule probes (illustrated actually,
by microscopes that do enjoy vastly higher resolutions than were state
of the art 10 years ago; and they can image complex atoms and small
molecules).

These scales are commonly referred to as 1D, or quantum dots. Now,
given a measurement must be made, it demands a probe. Further, given
a quantum dot sized probe, it necessarily describes the smallest size
for which any smaller size yields no more information.

The practicality of it is that this quantum dot would have to reside
at the end of a very thin lead. A carbon nanotube so qualifies, and
they can be grown to considerable length (for this field), and they
themselves occupy no more than 1nM diameter (for a single walled
construction which is not terribly difficult to obtain).

In the practical field of RF, I seriously doubt such a probe/lead
combination would perturb a slotted line. In fact, their influence
would be lost in the decimals far to the right of the accuracy of the
line's construction. Or, I could easily imagine that most computers
would suffer rounding errors long before the probe/lead's influence
could be calculated if the line were perfect.

Yes, for the absolutist (no speaking of you Owen), a probe could never
be small enough, but if it were smaller it would be impossible to
obtain a reading. Sort of self-extermination of the absolutist
argument.

73's
Richard Clark, KB7QHC