When it comes to measurements, most amateurs and very many
professionals suffer from delusions of accuracy.

Making measurements is an ART rather than an engineering discipline.

ALL measurements are subject to error. Errors are distributed in
magnitude between trivial and catastrophic. Much of the art lies in
assessment of the magnitude of error and depends on the
measurement-makers' judgement and experience. Indeed, honesty is a
factor.

To gain support for the validity of a measurement result by stating
the manufacturer's name and serial number of the instrument used
doesn't carry much weight since accuracy depends on the person who
made the measurement and many other just as important factors. People
can't be avoided.

Something similar applies to numerical computer programs. The
reliability of a computer program depends on the programmer's
knowledge of the matter in hand and has nothing to do with the machine
it is running on. Far too much faith is placed on computed results
merely because they are computed.

Very little extra knowledge is gained by comparing a pair of computed
and measured results because there is no means of knowing how and from
where the inevitable difference arises.

Reliabilty and confidence of both programs and measurements require
time in which to accumulate. Mean time between estimated errors?
----
Reg, G4FGQ

As we are fond of saying, "measure with a micrometer, mark with a crayola,
and cut with an axe"


"Reg Edwards" wrote in message
...
When it comes to measurements, most amateurs and very many
professionals suffer from delusions of accuracy.

Reg Edwards wrote:

-snip-

To gain support for the validity of a measurement result by stating
the manufacturer's name and serial number of the instrument used
doesn't carry much weight since accuracy depends on the person who
made the measurement and many other just as important factors. People
can't be avoided.

-snip-

I was taught to record ID information of all the tools and instruments
used, but I always took that to mean that it was to keep track of what
things to check if anomolies cropped up.

Having said that, if someone gives me a 5-digit voltage reading taken by
a 3-1/2 digit Rat Shack meter I'll believe it much less that if the
reading is taken by a recently calibrated name-brand 5-digit meter (and
I won't believe it much at any rate -- 5-digit voltage measurements have
_lots_ of embedded voodoo).

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Reg:

When ever you see charts being drug out and used as the basis for what
one is doing--you know you are in trouble.

Either the underlying laws and mathematical functions of that in
question are severely lacking--or the people you are dealing with do not
have the necessary skill--usually the former... here in radio you find a
lot of the latter...

From the abundance of charts laying around--I'd say there is still about
1/2 not known!

Warmest regards,
John



"Reg Edwards" wrote in message
...
When it comes to measurements, most amateurs and very many
professionals suffer from delusions of accuracy.

Making measurements is an ART rather than an engineering discipline.

ALL measurements are subject to error. Errors are distributed in
magnitude between trivial and catastrophic. Much of the art lies in
assessment of the magnitude of error and depends on the
measurement-makers' judgement and experience. Indeed, honesty is a
factor.

To gain support for the validity of a measurement result by stating
the manufacturer's name and serial number of the instrument used
doesn't carry much weight since accuracy depends on the person who
made the measurement and many other just as important factors. People
can't be avoided.

Something similar applies to numerical computer programs. The
reliability of a computer program depends on the programmer's
knowledge of the matter in hand and has nothing to do with the machine
it is running on. Far too much faith is placed on computed results
merely because they are computed.

Very little extra knowledge is gained by comparing a pair of computed
and measured results because there is no means of knowing how and from
where the inevitable difference arises.

Reliabilty and confidence of both programs and measurements require
time in which to accumulate. Mean time between estimated errors?
----
Reg, G4FGQ

Reg Edwards wrote:
. . .

Making measurements is an ART rather than an engineering discipline.

I maintain that it's both an art AND an engineering discipline.

. . .

Something similar applies to numerical computer programs. The
reliability of a computer program depends on the programmer's
knowledge of the matter in hand and has nothing to do with the machine
it is running on. Far too much faith is placed on computed results
merely because they are computed.

Agreed. This makes it essential that computed results be compared with
measured results, or results calculated by other established methods, to
gain confidence that the computer calculations are valid.

. . .
Very little extra knowledge is gained by comparing a pair of computed
and measured results because there is no means of knowing how and from
where the inevitable difference arises.
. . .

I've found that to be completely untrue. I've done a good deal of design
work in the areas of very high speed time domain circuitry and microwave
RF circuitry, where direct measurement of internal functioning is
impossible. I and my colleagues used modeling extensively in the course
of our design work. An essential part of the process is to periodically
look at the overall performance of a real circuit and compare it to the
model. The model was adjusted (by varying unknown values, by adding
components previously thought insignificant, and so forth) until the
model adequately matched the measured results. This does, of course,
require confidence in the measured results, which is subject to a host
of potential problems. But the important thing is that agreement between
the model and measurement must be gained in order to have any confidence
in the usefullness of the model. It's not only possible, but critical to
know how and from where the differences arise.

It sounds like you're saying that when presented with computed results
we have no recourse but to put faith in the programmer. That's not at
all so. We have to test the results against measurements or other
calculations and resolve the differences before we can put much faith in
any model or program.

With the rest, I agree.

. . .

Roy Lewallen, W7EL

Roy,
It sounds like you're saying that when presented with computed
results
we have no recourse but to put faith in the programmer. That's not
at
all so. We have to test the results against measurements or other
calculations and resolve the differences before we can put much
faith in
any model or program.

With the rest, I agree.

==================================

Roy, put a new battery in your hearing aid. ;o)

The danger of putting much faith in the programmer is that he may
belong to same set of old wives as the measurer and therefore make the
same mistakes. Misconceptions are known to be popular. The two sets
of incorrect results, measured and computed, then fatally agree with
each other due to the correlation.

It's impossible for a program to be more reliable than the programmer.
It can only be worse.

Your use of the word "before" implies a time span. The reliability of
anything accumulates with experience, use and TIME. (Don't anybody
mention bath tubs).

Reliability is Quality vs Time.

And Quality, in engineering terms, is the degree of conformance to
specified requirements. Or, in more worldly terms as may be applied
to computer programs, the fitness for the intended purpose.

Thus we can say that the accuracy of Eznec, etc., as determined over a
number of years, is highly fit for its intended purposes.
----
Reg, G4FGQ