Re: ATM horror story

[Stephen Tonkin <sft@aegis1.demon.co.uk>]

Robert Duvall <RDuvall@pixworks.com> wrote:
>I would just like to point out that the unfortunate error Stephen describes
>could very likely have been avoided by looking at the mirror with a Ronchi
>screen prior to doing the Foucault. 

With normal human beings, perhaps, but not with some single-minded sod
(no need to comment, Todd <g>) who instinctively uses the Ronchi screen
to check for quality (TDE/zones/smoothness of figure) but relies on
Foucault for something that approaches being quantitative.

I distinctly recall thinking, '*SURELY* those bands are curved enough
now!' and then checking the Foucault measurements only to "find" that
they weren't!

With the Ronchi test you do need to know what you're looking for (at
least, I do) and, although some instinct was trying to warn me, it was
my first fast mirror and I rushed to the Foucault test and the false
security of numbers.

Your point is well taken, though.


--
Stephen Tonkin