On Thu, 07 Aug 2003 13:34:34 +0100, Ian Iveson wrote:

Let's say you use your 4-channel scope to conveniently display
input, output, and two intermediate stages simultaneously. I
contend that when you look at your display, you compare traces in
pairs. This is not just a limitation of your eyes or your brain:
it is because there is no actual sense in comparing more than two
things. The question "What is the difference between these X
things?" only makes sense where X = 2.

You remind me of the people who insist
that nobody can visualize beyond three
dimensions, so there is no real use for
arrays of more than three dimensions.
Yet I've been both visualizing and using
arrays of more than 3d for decades. And
having no trouble teaching others to do
so. 8^)

I have to admit, I'm really more interested
in the number of inputs than the number of
traces. But the more the merrier. Even
with multiple traces (vs channels superimposed
on each other), it's often easier to grasp the
overall effect of what's happening, and see
how everything relates and impacts everything
else, if one has it all before the eyes at once.

There are (X-1)*X/2 differences between X things. You can sensibly
ask "What are the differences?" and these you may evaluate by
considering each possible pair. Hence, whatever comparison you
carry out with your 4-channel scope can be done with a maximum of 6
probe swaps with a dual-channel scope.

Which is an obscene amount of time. And if your
memory and visualization skills are less than
perfect, it's all to easy to forget exactly what
happened when, where and why, and thus miss
something crucial.

If you remember all your early maths, like long division and
multiplication, and even adding several numbers, that was all about
breaking the process down until you could deal with numbers in
pairs.

I coach people who dropped out of school,
and are going for their GED or into college,
on math. I think I get the concept! But
it doesn't apply that well here, IMO.

Just for grins, let's say you're trying to
show the effect of having two preamp
stages, with volume controls after each.
You can demonstrate how things work much
better, and much quicker, if you haev four
inputs. You can always kill two inputs to
focus in on any one stage, but you can also
show the overall picture *much* better with
those 4 inputs!

You're welcome to your opinion - but that's all
it is (just like mine 8^). And while you're busy
swapping probes, the guy with the 4 input scope
(soon to be me, I hope) will have resolved that
issue and gone on to something else.