It's time to restore the 11/45.

[Mouse]

>> With most 'scopes one side of the input is grounded [...]
> Ah.  That's the part I was missing!  I (naively :-) assumed that the
> 'scope's whole input amplifier would be 'floating', and the input
> signal would be taken as referenced to the 'ground' on the probe,
> which could itself be floating.

That amounts to a differential (rather than single-ended) input, and I
would consider that the _right_ way to do it.  But, of course, that
costs, and single-ended is plenty good enough for most purposes, so
that's what most scopes do. :-(

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